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 $38.37   13.393%   $43.5089   $43.51   $43.50   $43.50  
  Purchase #2 $159.31   10.179%   $175.5262   $175.53   $175.55   $175.50  
  Purchase #3 $88.64   4.502%   $92.6306   $92.63   $92.65   $92.60  
  Purchase #4 $65.70   6.580%   $70.0231   $70.02   $70.00   $70.00  
  Purchase #5 $183.67   13.238%   $207.9842   $207.98   $208.00   $208.00  
  Purchase #6 $127.32   11.340%   $141.7581   $141.76   $141.75   $141.80  
  Purchase #7 $139.94   9.370%   $153.0524   $153.05   $153.05   $153.10  
  7 purchase totals = $802.95       $884.4835   $884.48   $884.50   $884.50