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 $95.37   6.439%   $101.5109   $101.51   $101.50   $101.50  
  Purchase #2 $250.61   13.803%   $285.2017   $285.20   $285.20   $285.20  
  Purchase #3 $61.41   4.158%   $63.9634   $63.96   $63.95   $64.00  
  Purchase #4 $7.86   11.497%   $8.7637   $8.76   $8.75   $8.80  
  Purchase #5 $36.98   4.585%   $38.6755   $38.68   $38.70   $38.70  
  Purchase #6 $120.94   8.725%   $131.492   $131.49   $131.50   $131.50  
  Purchase #7 $23.83   3.846%   $24.7465   $24.75   $24.75   $24.70  
  7 purchase totals = $597.00       $654.3537   $654.35   $654.35   $654.40