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 $243.43   11.547%   $271.5389   $271.54   $271.55   $271.50  
  Purchase #2 $244.75   8.109%   $264.5968   $264.60   $264.60   $264.60  
  Purchase #3 $98.36   12.861%   $111.0101   $111.01   $111.00   $111.00  
  Purchase #4 $77.77   5.501%   $82.0481   $82.05   $82.05   $82.00  
  Purchase #5 $23.42   11.851%   $26.1955   $26.20   $26.20   $26.20  
  Purchase #6 $46.41   7.383%   $49.8365   $49.84   $49.85   $49.80  
  Purchase #7 $140.53   11.555%   $156.7682   $156.77   $156.75   $156.80  
  7 purchase totals = $874.67       $961.9941   $962.01   $962.00   $961.90