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 $241.34   11.674%   $269.514   $269.51   $269.50   $269.50  
  Purchase #2 $11.58   13.116%   $13.0988   $13.10   $13.10   $13.10  
  Purchase #3 $67.51   3.512%   $69.881   $69.88   $69.90   $69.90  
  Purchase #4 $113.26   10.834%   $125.5306   $125.53   $125.55   $125.50  
  Purchase #5 $94.49   5.259%   $99.4592   $99.46   $99.45   $99.50  
  Purchase #6 $124.48   3.375%   $128.6812   $128.68   $128.70   $128.70  
  Purchase #7 $228.50   7.841%   $246.4167   $246.42   $246.40   $246.40  
  7 purchase totals = $881.16       $952.5815   $952.58   $952.60   $952.60