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 $56.97   10.177%   $62.7678   $62.77   $62.75   $62.80  
  Purchase #2 $122.55   10.603%   $135.544   $135.54   $135.55   $135.50  
  Purchase #3 $91.71   11.822%   $102.552   $102.55   $102.55   $102.60  
  Purchase #4 $12.76   3.802%   $13.2451   $13.25   $13.25   $13.20  
  Purchase #5 $67.49   12.771%   $76.1091   $76.11   $76.10   $76.10  
  Purchase #6 $232.83   4.728%   $243.8382   $243.84   $243.85   $243.80  
  Purchase #7 $185.42   7.311%   $198.9761   $198.98   $199.00   $199.00  
  7 purchase totals = $769.73       $833.0323   $833.04   $833.05   $833.00