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 $88.67   6.310%   $94.2651   $94.27   $94.25   $94.30  
  Purchase #2 $33.97   3.539%   $35.1722   $35.17   $35.15   $35.20  
  Purchase #3 $153.73   13.620%   $174.668   $174.67   $174.65   $174.70  
  Purchase #4 $57.88   7.326%   $62.1203   $62.12   $62.10   $62.10  
  Purchase #5 $8.56   4.228%   $8.9219   $8.92   $8.90   $8.90  
  Purchase #6 $200.63   10.314%   $221.323   $221.32   $221.30   $221.30  
  Purchase #7 $60.38   7.151%   $64.6978   $64.70   $64.70   $64.70  
  7 purchase totals = $603.82       $661.1683   $661.17   $661.05   $661.20