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 $106.77   11.325%   $118.8617   $118.86   $118.85   $118.90  
  Purchase #2 $244.96   6.561%   $261.0318   $261.03   $261.05   $261.00  
  Purchase #3 $42.98   8.737%   $46.7352   $46.74   $46.75   $46.70  
  Purchase #4 $221.77   9.495%   $242.8271   $242.83   $242.85   $242.80  
  Purchase #5 $5.46   6.306%   $5.8043   $5.80   $5.80   $5.80  
  Purchase #6 $223.54   10.482%   $246.9715   $246.97   $246.95   $247.00  
  Purchase #7 $46.82   6.307%   $49.7729   $49.77   $49.75   $49.80  
  7 purchase totals = $892.30       $972.0045   $972.00   $972.00   $972.00