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 $70.61   8.123%   $76.3457   $76.35   $76.35   $76.30  
  Purchase #2 $242.75   10.443%   $268.1004   $268.10   $268.10   $268.10  
  Purchase #3 $71.50   8.504%   $77.5804   $77.58   $77.60   $77.60  
  Purchase #4 $25.69   10.310%   $28.3386   $28.34   $28.35   $28.30  
  Purchase #5 $239.61   9.214%   $261.6877   $261.69   $261.70   $261.70  
  Purchase #6 $52.78   10.715%   $58.4354   $58.44   $58.45   $58.40  
  Purchase #7 $92.47   4.281%   $96.4286   $96.43   $96.45   $96.40  
  7 purchase totals = $795.41       $866.9168   $866.93   $867.00   $866.80