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 $6.42   10.725%   $7.1085   $7.11   $7.10   $7.10  
  Purchase #2 $14.76   7.277%   $15.8341   $15.83   $15.85   $15.80  
  Purchase #3 $91.33   6.629%   $97.3843   $97.38   $97.40   $97.40  
  Purchase #4 $11.71   9.501%   $12.8226   $12.82   $12.80   $12.80  
  Purchase #5 $218.36   9.195%   $238.4382   $238.44   $238.45   $238.40  
  Purchase #6 $18.37   7.292%   $19.7095   $19.71   $19.70   $19.70  
  Purchase #7 $45.47   10.617%   $50.2975   $50.30   $50.30   $50.30  
  7 purchase totals = $406.42       $441.5947   $441.59   $441.60   $441.50