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 $170.70   13.836%   $194.3181   $194.32   $194.30   $194.30  
  Purchase #2 $197.27   9.138%   $215.2965   $215.30   $215.30   $215.30  
  Purchase #3 $246.33   5.647%   $260.2403   $260.24   $260.25   $260.20  
  Purchase #4 $162.85   4.335%   $169.9095   $169.91   $169.90   $169.90  
  Purchase #5 $217.29   12.848%   $245.2074   $245.21   $245.20   $245.20  
  Purchase #6 $173.42   13.676%   $197.1369   $197.14   $197.15   $197.10  
  Purchase #7 $36.52   12.820%   $41.2019   $41.20   $41.20   $41.20  
  7 purchase totals = $1,204.38       $1,323.3106   $1,323.32   $1,323.30   $1,323.20