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 $125.90   4.276%   $131.2835   $131.28   $131.30   $131.30  
  Purchase #2 $230.25   3.198%   $237.6134   $237.61   $237.60   $237.60  
  Purchase #3 $155.70   6.272%   $165.4655   $165.47   $165.45   $165.50  
  Purchase #4 $178.76   8.573%   $194.0851   $194.09   $194.10   $194.10  
  Purchase #5 $126.55   11.715%   $141.3753   $141.38   $141.40   $141.40  
  Purchase #6 $93.46   4.210%   $97.3947   $97.39   $97.40   $97.40  
  Purchase #7 $52.25   12.611%   $58.8392   $58.84   $58.85   $58.80  
  7 purchase totals = $962.87       $1,026.0567   $1,026.06   $1,026.10   $1,026.10