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 $178.75   9.321%   $195.4113   $195.41   $195.40   $195.40  
  Purchase #2 $233.83   3.248%   $241.4248   $241.42   $241.40   $241.40  
  Purchase #3 $84.71   5.561%   $89.4207   $89.42   $89.40   $89.40  
  Purchase #4 $18.41   9.302%   $20.1225   $20.12   $20.10   $20.10  
  Purchase #5 $77.26   7.373%   $82.9564   $82.96   $82.95   $83.00  
  Purchase #6 $167.64   11.368%   $186.6973   $186.70   $186.70   $186.70  
  Purchase #7 $58.89   6.567%   $62.7573   $62.76   $62.75   $62.80  
  7 purchase totals = $819.49       $878.7903   $878.79   $878.70   $878.80