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 $82.42   12.385%   $92.6277   $92.63   $92.65   $92.60  
  Purchase #2 $118.36   13.669%   $134.5386   $134.54   $134.55   $134.50  
  Purchase #3 $153.42   11.237%   $170.6598   $170.66   $170.65   $170.70  
  Purchase #4 $199.67   10.573%   $220.7811   $220.78   $220.80   $220.80  
  Purchase #5 $68.85   4.674%   $72.068   $72.07   $72.05   $72.10  
  Purchase #6 $31.48   6.144%   $33.4141   $33.41   $33.40   $33.40  
  Purchase #7 $24.95   10.438%   $27.5543   $27.55   $27.55   $27.60  
  7 purchase totals = $679.15       $751.6436   $751.64   $751.65   $751.70