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 $193.96   6.189%   $205.9642   $205.96   $205.95   $206.00  
  Purchase #2 $66.61   3.525%   $68.958   $68.96   $68.95   $69.00  
  Purchase #3 $47.43   7.126%   $50.8099   $50.81   $50.80   $50.80  
  Purchase #4 $151.55   5.795%   $160.3323   $160.33   $160.35   $160.30  
  Purchase #5 $122.59   8.319%   $132.7883   $132.79   $132.80   $132.80  
  Purchase #6 $113.42   5.211%   $119.3303   $119.33   $119.35   $119.30  
  Purchase #7 $195.51   10.652%   $216.3357   $216.34   $216.35   $216.30  
  7 purchase totals = $891.07       $954.5187   $954.52   $954.55   $954.50