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 $58.76   5.213%   $61.8232   $61.82   $61.80   $61.80  
  Purchase #2 $113.43   5.608%   $119.7912   $119.79   $119.80   $119.80  
  Purchase #3 $116.38   8.750%   $126.5633   $126.56   $126.55   $126.60  
  Purchase #4 $167.54   11.861%   $187.4119   $187.41   $187.40   $187.40  
  Purchase #5 $11.54   8.120%   $12.477   $12.48   $12.50   $12.50  
  Purchase #6 $187.92   10.316%   $207.3058   $207.31   $207.30   $207.30  
  Purchase #7 $242.37   13.192%   $274.3435   $274.34   $274.35   $274.30  
  7 purchase totals = $897.94       $989.7159   $989.71   $989.70   $989.70