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 $246.99   8.739%   $268.5745   $268.57   $268.55   $268.60  
  Purchase #2 $134.51   3.618%   $139.3766   $139.38   $139.40   $139.40  
  Purchase #3 $48.55   11.161%   $53.9687   $53.97   $53.95   $54.00  
  Purchase #4 $95.83   12.118%   $107.4427   $107.44   $107.45   $107.40  
  Purchase #5 $92.55   8.454%   $100.3742   $100.37   $100.35   $100.40  
  Purchase #6 $110.54   13.424%   $125.3789   $125.38   $125.40   $125.40  
  Purchase #7 $220.35   6.594%   $234.8799   $234.88   $234.90   $234.90  
  7 purchase totals = $949.32       $1,029.9955   $1,029.99   $1,030.00   $1,030.10