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 $186.80   8.272%   $202.2521   $202.25   $202.25   $202.30  
  Purchase #2 $160.89   8.496%   $174.5592   $174.56   $174.55   $174.60  
  Purchase #3 $110.39   13.332%   $125.1072   $125.11   $125.10   $125.10  
  Purchase #4 $91.43   9.174%   $99.8178   $99.82   $99.80   $99.80  
  Purchase #5 $22.44   8.145%   $24.2677   $24.27   $24.25   $24.30  
  Purchase #6 $167.69   3.448%   $173.472   $173.47   $173.45   $173.50  
  Purchase #7 $176.36   8.663%   $191.6381   $191.64   $191.65   $191.60  
  7 purchase totals = $916.00       $991.1141   $991.12   $991.05   $991.20