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 $57.90   5.610%   $61.1482   $61.15   $61.15   $61.10  
  Purchase #2 $168.81   6.217%   $179.3049   $179.30   $179.30   $179.30  
  Purchase #3 $104.80   6.152%   $111.2473   $111.25   $111.25   $111.20  
  Purchase #4 $5.72   4.406%   $5.972   $5.97   $5.95   $6.00  
  Purchase #5 $249.89   4.223%   $260.4429   $260.44   $260.45   $260.40  
  Purchase #6 $240.46   11.220%   $267.4396   $267.44   $267.45   $267.40  
  Purchase #7 $118.32   5.466%   $124.7874   $124.79   $124.80   $124.80  
  7 purchase totals = $945.90       $1,010.3423   $1,010.34   $1,010.35   $1,010.20