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 $94.53   5.279%   $99.5202   $99.52   $99.50   $99.50  
  Purchase #2 $246.32   6.322%   $261.8924   $261.89   $261.90   $261.90  
  Purchase #3 $190.62   3.384%   $197.0706   $197.07   $197.05   $197.10  
  Purchase #4 $116.64   4.354%   $121.7185   $121.72   $121.70   $121.70  
  Purchase #5 $99.29   9.413%   $108.6362   $108.64   $108.65   $108.60  
  Purchase #6 $58.69   5.623%   $61.9901   $61.99   $62.00   $62.00  
  Purchase #7 $53.57   3.187%   $55.2773   $55.28   $55.30   $55.30  
  7 purchase totals = $859.66       $906.1053   $906.11   $906.10   $906.10