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 $133.65   10.683%   $147.9278   $147.93   $147.95   $147.90  
  Purchase #2 $70.82   8.381%   $76.7554   $76.76   $76.75   $76.80  
  Purchase #3 $69.80   8.218%   $75.5362   $75.54   $75.55   $75.50  
  Purchase #4 $120.67   3.798%   $125.253   $125.25   $125.25   $125.30  
  Purchase #5 $72.90   12.407%   $81.9447   $81.94   $81.95   $81.90  
  Purchase #6 $70.98   3.636%   $73.5608   $73.56   $73.55   $73.60  
  Purchase #7 $165.51   3.533%   $171.3575   $171.36   $171.35   $171.40  
  7 purchase totals = $704.33       $752.3354   $752.34   $752.35   $752.40