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 $207.56   6.521%   $221.095   $221.10   $221.10   $221.10  
  Purchase #2 $232.33   3.858%   $241.2933   $241.29   $241.30   $241.30  
  Purchase #3 $16.70   5.784%   $17.6659   $17.67   $17.65   $17.70  
  Purchase #4 $185.94   7.498%   $199.8818   $199.88   $199.90   $199.90  
  Purchase #5 $83.82   10.163%   $92.3386   $92.34   $92.35   $92.30  
  Purchase #6 $173.49   11.647%   $193.6964   $193.70   $193.70   $193.70  
  Purchase #7 $51.38   4.512%   $53.6983   $53.70   $53.70   $53.70  
  7 purchase totals = $951.22       $1,019.6693   $1,019.68   $1,019.70   $1,019.70