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 $172.32   11.617%   $192.3384   $192.34   $192.35   $192.30  
  Purchase #2 $185.74   4.126%   $193.4036   $193.40   $193.40   $193.40  
  Purchase #3 $219.70   12.668%   $247.5316   $247.53   $247.55   $247.50  
  Purchase #4 $183.67   4.394%   $191.7405   $191.74   $191.75   $191.70  
  Purchase #5 $175.37   3.754%   $181.9534   $181.95   $181.95   $182.00  
  Purchase #6 $98.61   11.422%   $109.8732   $109.87   $109.85   $109.90  
  Purchase #7 $141.78   7.646%   $152.6205   $152.62   $152.60   $152.60  
  7 purchase totals = $1,177.19       $1,269.4612   $1,269.45   $1,269.45   $1,269.40