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 $200.39   4.773%   $209.9546   $209.95   $209.95   $210.00  
  Purchase #2 $164.56   8.423%   $178.4209   $178.42   $178.40   $178.40  
  Purchase #3 $53.76   11.556%   $59.9725   $59.97   $59.95   $60.00  
  Purchase #4 $249.32   9.207%   $272.2749   $272.27   $272.25   $272.30  
  Purchase #5 $239.52   13.414%   $271.6492   $271.65   $271.65   $271.60  
  Purchase #6 $242.42   12.282%   $272.194   $272.19   $272.20   $272.20  
  Purchase #7 $169.70   12.763%   $191.3588   $191.36   $191.35   $191.40  
  7 purchase totals = $1,319.67       $1,455.8249   $1,455.81   $1,455.75   $1,455.90