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 $88.61   6.643%   $94.4964   $94.50   $94.50   $94.50  
  Purchase #2 $213.35   10.421%   $235.5832   $235.58   $235.60   $235.60  
  Purchase #3 $10.66   7.871%   $11.499   $11.50   $11.50   $11.50  
  Purchase #4 $98.38   7.557%   $105.8146   $105.81   $105.80   $105.80  
  Purchase #5 $70.43   13.873%   $80.2008   $80.20   $80.20   $80.20  
  Purchase #6 $135.84   9.407%   $148.6185   $148.62   $148.60   $148.60  
  Purchase #7 $100.52   4.337%   $104.8796   $104.88   $104.90   $104.90  
  7 purchase totals = $717.79       $781.0921   $781.09   $781.10   $781.10