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 $213.38   6.361%   $226.9531   $226.95   $226.95   $227.00  
  Purchase #2 $229.36   9.153%   $250.3533   $250.35   $250.35   $250.40  
  Purchase #3 $249.64   8.551%   $270.9867   $270.99   $271.00   $271.00  
  Purchase #4 $111.45   13.368%   $126.3486   $126.35   $126.35   $126.30  
  Purchase #5 $165.79   3.186%   $171.0721   $171.07   $171.05   $171.10  
  Purchase #6 $212.65   7.103%   $227.7545   $227.75   $227.75   $227.80  
  Purchase #7 $75.94   7.485%   $81.6241   $81.62   $81.60   $81.60  
  7 purchase totals = $1,258.21       $1,355.0924   $1,355.08   $1,355.05   $1,355.20