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 $56.63   9.197%   $61.8383   $61.84   $61.85   $61.80  
  Purchase #2 $18.26   9.643%   $20.0208   $20.02   $20.00   $20.00  
  Purchase #3 $14.54   7.818%   $15.6767   $15.68   $15.70   $15.70  
  Purchase #4 $54.25   4.389%   $56.631   $56.63   $56.65   $56.60  
  Purchase #5 $5.45   13.596%   $6.191   $6.19   $6.20   $6.20  
  Purchase #6 $29.45   9.724%   $32.3137   $32.31   $32.30   $32.30  
  Purchase #7 $95.67   7.453%   $102.8003   $102.80   $102.80   $102.80  
  7 purchase totals = $274.25       $295.4718   $295.47   $295.50   $295.40