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 $63.53   8.407%   $68.871   $68.87   $68.85   $68.90  
  Purchase #2 $55.71   12.793%   $62.837   $62.84   $62.85   $62.80  
  Purchase #3 $14.95   5.497%   $15.7718   $15.77   $15.75   $15.80  
  Purchase #4 $235.34   6.254%   $250.0582   $250.06   $250.05   $250.10  
  Purchase #5 $235.87   7.709%   $254.0532   $254.05   $254.05   $254.10  
  Purchase #6 $229.68   13.193%   $259.9817   $259.98   $260.00   $260.00  
  Purchase #7 $124.58   9.675%   $136.6331   $136.63   $136.65   $136.60  
  7 purchase totals = $959.66       $1,048.2060   $1,048.20   $1,048.20   $1,048.30