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 $53.86   13.443%   $61.1004   $61.10   $61.10   $61.10  
  Purchase #2 $83.97   4.689%   $87.9074   $87.91   $87.90   $87.90  
  Purchase #3 $104.56   10.361%   $115.3935   $115.39   $115.40   $115.40  
  Purchase #4 $243.93   3.742%   $253.0579   $253.06   $253.05   $253.10  
  Purchase #5 $25.42   6.857%   $27.163   $27.16   $27.15   $27.20  
  Purchase #6 $25.42   7.295%   $27.2744   $27.27   $27.25   $27.30  
  Purchase #7 $191.57   11.377%   $213.3649   $213.36   $213.35   $213.40  
  7 purchase totals = $728.73       $785.2615   $785.25   $785.20   $785.40