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 $68.79   11.713%   $76.8474   $76.85   $76.85   $76.80  
  Purchase #2 $232.96   8.156%   $251.9602   $251.96   $251.95   $252.00  
  Purchase #3 $72.45   7.536%   $77.9098   $77.91   $77.90   $77.90  
  Purchase #4 $35.56   11.145%   $39.5232   $39.52   $39.50   $39.50  
  Purchase #5 $22.31   7.121%   $23.8987   $23.90   $23.90   $23.90  
  Purchase #6 $132.89   5.479%   $140.171   $140.17   $140.15   $140.20  
  Purchase #7 $170.42   8.802%   $185.4204   $185.42   $185.40   $185.40  
  7 purchase totals = $735.38       $795.7307   $795.73   $795.65   $795.70