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 $191.27   3.657%   $198.2647   $198.26   $198.25   $198.30  
  Purchase #2 $26.38   7.242%   $28.2904   $28.29   $28.30   $28.30  
  Purchase #3 $151.59   11.761%   $169.4185   $169.42   $169.40   $169.40  
  Purchase #4 $248.47   8.104%   $268.606   $268.61   $268.60   $268.60  
  Purchase #5 $246.70   13.125%   $279.0794   $279.08   $279.10   $279.10  
  Purchase #6 $165.44   3.169%   $170.6828   $170.68   $170.70   $170.70  
  Purchase #7 $223.43   10.177%   $246.1685   $246.17   $246.15   $246.20  
  7 purchase totals = $1,253.28       $1,360.5103   $1,360.51   $1,360.50   $1,360.60