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 $75.87   11.462%   $84.5662   $84.57   $84.55   $84.60  
  Purchase #2 $53.65   13.756%   $61.0301   $61.03   $61.05   $61.00  
  Purchase #3 $203.80   8.284%   $220.6828   $220.68   $220.70   $220.70  
  Purchase #4 $94.96   5.865%   $100.5294   $100.53   $100.55   $100.50  
  Purchase #5 $133.73   4.198%   $139.344   $139.34   $139.35   $139.30  
  Purchase #6 $113.35   13.824%   $129.0195   $129.02   $129.00   $129.00  
  Purchase #7 $24.65   12.234%   $27.6657   $27.67   $27.65   $27.70  
  7 purchase totals = $700.01       $762.8377   $762.84   $762.85   $762.80