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 $216.73   8.788%   $235.7762   $235.78   $235.80   $235.80  
  Purchase #2 $21.99   10.545%   $24.3088   $24.31   $24.30   $24.30  
  Purchase #3 $58.42   4.316%   $60.9414   $60.94   $60.95   $60.90  
  Purchase #4 $61.48   11.399%   $68.4881   $68.49   $68.50   $68.50  
  Purchase #5 $202.43   13.264%   $229.2803   $229.28   $229.30   $229.30  
  Purchase #6 $20.62   7.739%   $22.2158   $22.22   $22.20   $22.20  
  Purchase #7 $70.85   3.310%   $73.1951   $73.20   $73.20   $73.20  
  7 purchase totals = $652.52       $714.2057   $714.22   $714.25   $714.20