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 $204.33   11.201%   $227.217   $227.22   $227.20   $227.20  
  Purchase #2 $234.83   13.275%   $266.0037   $266.00   $266.00   $266.00  
  Purchase #3 $155.71   11.158%   $173.0841   $173.08   $173.10   $173.10  
  Purchase #4 $68.98   6.626%   $73.5506   $73.55   $73.55   $73.60  
  Purchase #5 $248.46   13.399%   $281.7512   $281.75   $281.75   $281.80  
  Purchase #6 $161.34   7.157%   $172.8871   $172.89   $172.90   $172.90  
  Purchase #7 $210.68   6.180%   $223.7   $223.70   $223.70   $223.70  
  7 purchase totals = $1,284.33       $1,418.1937   $1,418.19   $1,418.20   $1,418.30