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 $93.53   4.398%   $97.6434   $97.64   $97.65   $97.60  
  Purchase #2 $113.64   11.281%   $126.4597   $126.46   $126.45   $126.50  
  Purchase #3 $167.73   13.304%   $190.0448   $190.04   $190.05   $190.00  
  Purchase #4 $194.38   11.437%   $216.6112   $216.61   $216.60   $216.60  
  Purchase #5 $117.37   9.683%   $128.7349   $128.73   $128.75   $128.70  
  Purchase #6 $211.65   8.361%   $229.3461   $229.35   $229.35   $229.30  
  Purchase #7 $250.52   11.127%   $278.3954   $278.40   $278.40   $278.40  
  7 purchase totals = $1,148.82       $1,267.2355   $1,267.23   $1,267.25   $1,267.10