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 $49.58   12.655%   $55.8543   $55.85   $55.85   $55.90  
  Purchase #2 $56.97   8.434%   $61.7748   $61.77   $61.75   $61.80  
  Purchase #3 $206.34   11.538%   $230.1475   $230.15   $230.15   $230.10  
  Purchase #4 $56.90   4.638%   $59.539   $59.54   $59.55   $59.50  
  Purchase #5 $162.93   6.694%   $173.8365   $173.84   $173.85   $173.80  
  Purchase #6 $54.97   12.833%   $62.0243   $62.02   $62.00   $62.00  
  Purchase #7 $214.58   8.476%   $232.7678   $232.77   $232.75   $232.80  
  7 purchase totals = $802.27       $875.9442   $875.94   $875.90   $875.90