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 $236.58   7.474%   $254.262   $254.26   $254.25   $254.30  
  Purchase #2 $153.60   13.184%   $173.8506   $173.85   $173.85   $173.90  
  Purchase #3 $148.58   8.171%   $160.7205   $160.72   $160.70   $160.70  
  Purchase #4 $126.75   3.649%   $131.3751   $131.38   $131.40   $131.40  
  Purchase #5 $28.96   12.340%   $32.5337   $32.53   $32.55   $32.50  
  Purchase #6 $60.94   4.616%   $63.753   $63.75   $63.75   $63.80  
  Purchase #7 $65.91   12.248%   $73.9827   $73.98   $74.00   $74.00  
  7 purchase totals = $821.32       $890.4776   $890.47   $890.50   $890.60