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 $34.32   3.512%   $35.5253   $35.53   $35.55   $35.50  
  Purchase #2 $52.33   11.661%   $58.4322   $58.43   $58.45   $58.40  
  Purchase #3 $213.49   12.506%   $240.1891   $240.19   $240.20   $240.20  
  Purchase #4 $198.80   5.224%   $209.1853   $209.19   $209.20   $209.20  
  Purchase #5 $146.50   4.139%   $152.5636   $152.56   $152.55   $152.60  
  Purchase #6 $5.76   4.291%   $6.0072   $6.01   $6.00   $6.00  
  Purchase #7 $44.71   13.598%   $50.7897   $50.79   $50.80   $50.80  
  7 purchase totals = $695.91       $752.6924   $752.70   $752.75   $752.70