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 $241.56   9.582%   $264.7063   $264.71   $264.70   $264.70  
  Purchase #2 $5.90   3.572%   $6.1107   $6.11   $6.10   $6.10  
  Purchase #3 $113.82   11.136%   $126.495   $126.50   $126.50   $126.50  
  Purchase #4 $44.73   6.277%   $47.5377   $47.54   $47.55   $47.50  
  Purchase #5 $123.37   10.684%   $136.5509   $136.55   $136.55   $136.60  
  Purchase #6 $178.66   3.294%   $184.5451   $184.55   $184.55   $184.50  
  Purchase #7 $41.63   3.601%   $43.1291   $43.13   $43.15   $43.10  
  7 purchase totals = $749.67       $809.0748   $809.09   $809.10   $809.00