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 $237.54   11.559%   $264.9972   $265.00   $265.00   $265.00  
  Purchase #2 $43.37   7.175%   $46.4818   $46.48   $46.50   $46.50  
  Purchase #3 $201.36   3.771%   $208.9533   $208.95   $208.95   $209.00  
  Purchase #4 $56.25   6.804%   $60.0773   $60.08   $60.10   $60.10  
  Purchase #5 $199.78   12.632%   $225.0162   $225.02   $225.00   $225.00  
  Purchase #6 $108.91   7.154%   $116.7014   $116.70   $116.70   $116.70  
  Purchase #7 $198.61   13.659%   $225.7381   $225.74   $225.75   $225.70  
  7 purchase totals = $1,045.82       $1,147.9653   $1,147.97   $1,148.00   $1,148.00