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 $141.56   8.217%   $153.192   $153.19   $153.20   $153.20  
  Purchase #2 $189.63   6.808%   $202.54   $202.54   $202.55   $202.50  
  Purchase #3 $125.43   12.104%   $140.612   $140.61   $140.60   $140.60  
  Purchase #4 $36.56   8.165%   $39.5451   $39.55   $39.55   $39.50  
  Purchase #5 $129.65   5.423%   $136.6809   $136.68   $136.70   $136.70  
  Purchase #6 $196.82   11.847%   $220.1373   $220.14   $220.15   $220.10  
  Purchase #7 $96.97   4.626%   $101.4558   $101.46   $101.45   $101.50  
  7 purchase totals = $916.62       $994.1631   $994.17   $994.20   $994.10