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 $88.65   11.370%   $98.7295   $98.73   $98.75   $98.70  
  Purchase #2 $214.76   12.663%   $241.9551   $241.96   $241.95   $242.00  
  Purchase #3 $159.88   9.495%   $175.0606   $175.06   $175.05   $175.10  
  Purchase #4 $186.93   10.256%   $206.1015   $206.10   $206.10   $206.10  
  Purchase #5 $98.89   13.692%   $112.43   $112.43   $112.45   $112.40  
  Purchase #6 $147.71   13.490%   $167.6361   $167.64   $167.65   $167.60  
  Purchase #7 $250.40   10.417%   $276.4842   $276.48   $276.50   $276.50  
  7 purchase totals = $1,147.22       $1,278.3970   $1,278.40   $1,278.45   $1,278.40