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 $38.62   12.327%   $43.3807   $43.38   $43.40   $43.40  
  Purchase #2 $159.94   8.498%   $173.5317   $173.53   $173.55   $173.50  
  Purchase #3 $60.46   12.717%   $68.1487   $68.15   $68.15   $68.10  
  Purchase #4 $184.35   12.333%   $207.0859   $207.09   $207.10   $207.10  
  Purchase #5 $186.46   4.246%   $194.3771   $194.38   $194.40   $194.40  
  Purchase #6 $195.52   12.214%   $219.4008   $219.40   $219.40   $219.40  
  Purchase #7 $176.46   5.824%   $186.737   $186.74   $186.75   $186.70  
  7 purchase totals = $1,001.81       $1,092.6619   $1,092.67   $1,092.75   $1,092.60