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 $39.81   6.812%   $42.5219   $42.52   $42.50   $42.50  
  Purchase #2 $114.42   7.216%   $122.6765   $122.68   $122.70   $122.70  
  Purchase #3 $231.77   5.526%   $244.5776   $244.58   $244.60   $244.60  
  Purchase #4 $39.97   6.352%   $42.5089   $42.51   $42.50   $42.50  
  Purchase #5 $48.72   12.832%   $54.9718   $54.97   $54.95   $55.00  
  Purchase #6 $188.78   3.191%   $194.804   $194.80   $194.80   $194.80  
  Purchase #7 $213.81   3.306%   $220.8786   $220.88   $220.90   $220.90  
  7 purchase totals = $877.28       $922.9393   $922.94   $922.95   $923.00