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 $226.57   11.293%   $252.1566   $252.16   $252.15   $252.20  
  Purchase #2 $69.28   9.682%   $75.9877   $75.99   $76.00   $76.00  
  Purchase #3 $119.91   6.642%   $127.8744   $127.87   $127.85   $127.90  
  Purchase #4 $114.82   13.766%   $130.6261   $130.63   $130.65   $130.60  
  Purchase #5 $124.58   5.500%   $131.4319   $131.43   $131.45   $131.40  
  Purchase #6 $245.38   12.152%   $275.1986   $275.20   $275.20   $275.20  
  Purchase #7 $31.60   8.447%   $34.2693   $34.27   $34.25   $34.30  
  7 purchase totals = $932.14       $1,027.5446   $1,027.55   $1,027.55   $1,027.60