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 $201.39   13.545%   $228.6683   $228.67   $228.65   $228.70  
  Purchase #2 $178.82   4.822%   $187.4427   $187.44   $187.45   $187.40  
  Purchase #3 $111.68   4.353%   $116.5414   $116.54   $116.55   $116.50  
  Purchase #4 $39.30   8.788%   $42.7537   $42.75   $42.75   $42.80  
  Purchase #5 $187.82   8.599%   $203.9706   $203.97   $203.95   $204.00  
  Purchase #6 $237.38   4.580%   $248.252   $248.25   $248.25   $248.30  
  Purchase #7 $87.42   11.107%   $97.1297   $97.13   $97.15   $97.10  
  7 purchase totals = $1,043.81       $1,124.7584   $1,124.75   $1,124.75   $1,124.80