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 $71.82   13.489%   $81.5078   $81.51   $81.50   $81.50  
  Purchase #2 $248.92   9.137%   $271.6638   $271.66   $271.65   $271.70  
  Purchase #3 $25.89   3.847%   $26.886   $26.89   $26.90   $26.90  
  Purchase #4 $185.42   10.690%   $205.2414   $205.24   $205.25   $205.20  
  Purchase #5 $68.88   5.532%   $72.6904   $72.69   $72.70   $72.70  
  Purchase #6 $162.51   8.271%   $175.9512   $175.95   $175.95   $176.00  
  Purchase #7 $69.98   7.695%   $75.365   $75.37   $75.35   $75.40  
  7 purchase totals = $833.42       $909.3056   $909.31   $909.30   $909.40