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 $63.47   8.779%   $69.042   $69.04   $69.05   $69.00  
  Purchase #2 $211.30   6.250%   $224.5063   $224.51   $224.50   $224.50  
  Purchase #3 $77.65   7.430%   $83.4194   $83.42   $83.40   $83.40  
  Purchase #4 $152.82   5.288%   $160.9011   $160.90   $160.90   $160.90  
  Purchase #5 $225.62   6.618%   $240.5515   $240.55   $240.55   $240.60  
  Purchase #6 $172.25   6.114%   $182.7814   $182.78   $182.80   $182.80  
  Purchase #7 $236.58   6.324%   $251.5413   $251.54   $251.55   $251.50  
  7 purchase totals = $1,139.69       $1,212.7430   $1,212.74   $1,212.75   $1,212.70