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 $236.97   7.725%   $255.2759   $255.28   $255.30   $255.30  
  Purchase #2 $23.45   3.452%   $24.2595   $24.26   $24.25   $24.30  
  Purchase #3 $83.46   9.760%   $91.6057   $91.61   $91.60   $91.60  
  Purchase #4 $6.67   4.334%   $6.9591   $6.96   $6.95   $7.00  
  Purchase #5 $98.97   6.501%   $105.404   $105.40   $105.40   $105.40  
  Purchase #6 $232.80   5.278%   $245.0872   $245.09   $245.10   $245.10  
  Purchase #7 $99.47   5.242%   $104.6842   $104.68   $104.70   $104.70  
  7 purchase totals = $781.79       $833.2756   $833.28   $833.30   $833.40