Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $181.88   6.409%   $193.5367   $193.54   $193.55   $193.50  
  Purchase #2 $152.44   10.346%   $168.2114   $168.21   $168.20   $168.20  
  Purchase #3 $109.38   6.584%   $116.5816   $116.58   $116.60   $116.60  
  Purchase #4 $236.42   6.250%   $251.1963   $251.20   $251.20   $251.20  
  Purchase #5 $186.66   6.781%   $199.3174   $199.32   $199.30   $199.30  
  Purchase #6 $182.45   10.616%   $201.8189   $201.82   $201.80   $201.80  
  Purchase #7 $244.58   12.837%   $275.9767   $275.98   $276.00   $276.00  
  7 purchase totals = $1,293.81       $1,406.6390   $1,406.65   $1,406.65   $1,406.60