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 $244.27   9.726%   $268.0277   $268.03   $268.05   $268.00  
  Purchase #2 $124.58   5.667%   $131.6399   $131.64   $131.65   $131.60  
  Purchase #3 $19.43   5.343%   $20.4681   $20.47   $20.45   $20.50  
  Purchase #4 $197.65   6.760%   $211.0111   $211.01   $211.00   $211.00  
  Purchase #5 $42.73   5.235%   $44.9669   $44.97   $44.95   $45.00  
  Purchase #6 $140.81   11.650%   $157.2144   $157.21   $157.20   $157.20  
  Purchase #7 $19.75   9.726%   $21.6709   $21.67   $21.65   $21.70  
  7 purchase totals = $789.22       $854.9990   $855.00   $854.95   $855.00