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 $84.47   12.596%   $95.1098   $95.11   $95.10   $95.10  
  Purchase #2 $150.71   7.458%   $161.95   $161.95   $161.95   $162.00  
  Purchase #3 $133.79   9.500%   $146.5001   $146.50   $146.50   $146.50  
  Purchase #4 $132.59   8.760%   $144.2049   $144.20   $144.20   $144.20  
  Purchase #5 $178.71   12.350%   $200.7807   $200.78   $200.80   $200.80  
  Purchase #6 $178.48   3.159%   $184.1182   $184.12   $184.10   $184.10  
  Purchase #7 $16.67   3.710%   $17.2885   $17.29   $17.30   $17.30  
  7 purchase totals = $875.42       $949.9522   $949.95   $949.95   $950.00