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 $248.49   13.307%   $281.5566   $281.56   $281.55   $281.60  
  Purchase #2 $47.25   12.694%   $53.2479   $53.25   $53.25   $53.20  
  Purchase #3 $83.59   3.754%   $86.728   $86.73   $86.75   $86.70  
  Purchase #4 $245.31   9.752%   $269.2326   $269.23   $269.25   $269.20  
  Purchase #5 $66.82   3.219%   $68.9709   $68.97   $68.95   $69.00  
  Purchase #6 $167.59   9.804%   $184.0205   $184.02   $184.00   $184.00  
  Purchase #7 $77.97   13.790%   $88.7221   $88.72   $88.70   $88.70  
  7 purchase totals = $937.02       $1,032.4786   $1,032.48   $1,032.45   $1,032.40