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 $91.87   3.111%   $94.7281   $94.73   $94.75   $94.70  
  Purchase #2 $99.69   3.487%   $103.1662   $103.17   $103.15   $103.20  
  Purchase #3 $15.57   4.277%   $16.2359   $16.24   $16.25   $16.20  
  Purchase #4 $92.53   5.274%   $97.41   $97.41   $97.40   $97.40  
  Purchase #5 $190.65   11.681%   $212.9198   $212.92   $212.90   $212.90  
  Purchase #6 $151.67   10.307%   $167.3026   $167.30   $167.30   $167.30  
  Purchase #7 $9.37   12.697%   $10.5597   $10.56   $10.55   $10.60  
  7 purchase totals = $651.35       $702.3223   $702.33   $702.30   $702.30