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 $60.56   8.198%   $65.5247   $65.52   $65.50   $65.50  
  Purchase #2 $196.96   5.583%   $207.9563   $207.96   $207.95   $208.00  
  Purchase #3 $38.75   4.314%   $40.4217   $40.42   $40.40   $40.40  
  Purchase #4 $245.89   8.512%   $266.8202   $266.82   $266.80   $266.80  
  Purchase #5 $146.70   5.163%   $154.2741   $154.27   $154.25   $154.30  
  Purchase #6 $198.86   13.758%   $226.2192   $226.22   $226.20   $226.20  
  Purchase #7 $85.43   7.272%   $91.6425   $91.64   $91.65   $91.60  
  7 purchase totals = $973.15       $1,052.8587   $1,052.85   $1,052.75   $1,052.80