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 $129.35   13.545%   $146.8705   $146.87   $146.85   $146.90  
  Purchase #2 $44.93   6.361%   $47.788   $47.79   $47.80   $47.80  
  Purchase #3 $52.43   11.265%   $58.3362   $58.34   $58.35   $58.30  
  Purchase #4 $39.25   13.702%   $44.628   $44.63   $44.65   $44.60  
  Purchase #5 $234.98   12.473%   $264.2891   $264.29   $264.30   $264.30  
  Purchase #6 $66.36   6.762%   $70.8473   $70.85   $70.85   $70.80  
  Purchase #7 $113.67   10.866%   $126.0214   $126.02   $126.00   $126.00  
  7 purchase totals = $680.97       $758.7805   $758.79   $758.80   $758.70