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 $52.69   9.189%   $57.5317   $57.53   $57.55   $57.50  
  Purchase #2 $74.35   3.490%   $76.9448   $76.94   $76.95   $76.90  
  Purchase #3 $183.47   12.420%   $206.257   $206.26   $206.25   $206.30  
  Purchase #4 $234.68   13.319%   $265.937   $265.94   $265.95   $265.90  
  Purchase #5 $33.32   12.485%   $37.48   $37.48   $37.50   $37.50  
  Purchase #6 $222.70   5.665%   $235.316   $235.32   $235.30   $235.30  
  Purchase #7 $71.84   5.107%   $75.5089   $75.51   $75.50   $75.50  
  7 purchase totals = $873.05       $954.9754   $954.98   $955.00   $954.90