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 $44.26   12.233%   $49.6743   $49.67   $49.65   $49.70  
  Purchase #2 $99.94   8.594%   $108.5288   $108.53   $108.55   $108.50  
  Purchase #3 $34.83   5.147%   $36.6227   $36.62   $36.60   $36.60  
  Purchase #4 $130.98   8.259%   $141.7976   $141.80   $141.80   $141.80  
  Purchase #5 $107.77   6.830%   $115.1307   $115.13   $115.15   $115.10  
  Purchase #6 $232.36   5.836%   $245.9205   $245.92   $245.90   $245.90  
  Purchase #7 $62.36   11.369%   $69.4497   $69.45   $69.45   $69.40  
  7 purchase totals = $712.50       $767.1243   $767.12   $767.10   $767.00