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 $58.46   10.647%   $64.6842   $64.68   $64.70   $64.70  
  Purchase #2 $88.55   10.532%   $97.8761   $97.88   $97.90   $97.90  
  Purchase #3 $139.84   8.587%   $151.8481   $151.85   $151.85   $151.80  
  Purchase #4 $56.36   7.285%   $60.4658   $60.47   $60.45   $60.50  
  Purchase #5 $221.26   3.778%   $229.6192   $229.62   $229.60   $229.60  
  Purchase #6 $174.47   10.740%   $193.2081   $193.21   $193.20   $193.20  
  Purchase #7 $67.47   7.325%   $72.4122   $72.41   $72.40   $72.40  
  7 purchase totals = $806.41       $870.1137   $870.12   $870.10   $870.10