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 $213.73   5.786%   $226.0964   $226.10   $226.10   $226.10  
  Purchase #2 $180.73   12.309%   $202.9761   $202.98   $203.00   $203.00  
  Purchase #3 $159.38   4.858%   $167.1227   $167.12   $167.10   $167.10  
  Purchase #4 $157.41   12.170%   $176.5668   $176.57   $176.55   $176.60  
  Purchase #5 $122.73   11.207%   $136.4844   $136.48   $136.50   $136.50  
  Purchase #6 $73.94   3.197%   $76.3039   $76.30   $76.30   $76.30  
  Purchase #7 $166.76   7.491%   $179.252   $179.25   $179.25   $179.30  
  7 purchase totals = $1,074.68       $1,164.8023   $1,164.80   $1,164.80   $1,164.90