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 $44.73   11.666%   $49.9482   $49.95   $49.95   $49.90  
  Purchase #2 $134.59   12.726%   $151.7179   $151.72   $151.70   $151.70  
  Purchase #3 $147.97   3.122%   $152.5896   $152.59   $152.60   $152.60  
  Purchase #4 $207.75   3.404%   $214.8218   $214.82   $214.80   $214.80  
  Purchase #5 $26.52   9.455%   $29.0275   $29.03   $29.05   $29.00  
  Purchase #6 $215.64   9.505%   $236.1366   $236.14   $236.15   $236.10  
  Purchase #7 $134.84   5.688%   $142.5097   $142.51   $142.50   $142.50  
  7 purchase totals = $912.04       $976.7513   $976.76   $976.75   $976.60