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 $108.31   10.119%   $119.2699   $119.27   $119.25   $119.30  
  Purchase #2 $96.28   4.113%   $100.24   $100.24   $100.25   $100.20  
  Purchase #3 $54.62   11.677%   $60.998   $61.00   $61.00   $61.00  
  Purchase #4 $174.75   4.749%   $183.0489   $183.05   $183.05   $183.00  
  Purchase #5 $58.41   4.148%   $60.8328   $60.83   $60.85   $60.80  
  Purchase #6 $17.46   4.196%   $18.1926   $18.19   $18.20   $18.20  
  Purchase #7 $78.96   4.514%   $82.5243   $82.52   $82.50   $82.50  
  7 purchase totals = $588.79       $625.1065   $625.10   $625.10   $625.00