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 $67.91   13.337%   $76.9672   $76.97   $76.95   $77.00  
  Purchase #2 $35.87   11.323%   $39.9316   $39.93   $39.95   $39.90  
  Purchase #3 $99.87   7.435%   $107.2953   $107.30   $107.30   $107.30  
  Purchase #4 $150.66   10.378%   $166.2955   $166.30   $166.30   $166.30  
  Purchase #5 $124.92   11.287%   $139.0197   $139.02   $139.00   $139.00  
  Purchase #6 $157.40   10.729%   $174.2874   $174.29   $174.30   $174.30  
  Purchase #7 $26.43   7.287%   $28.356   $28.36   $28.35   $28.40  
  7 purchase totals = $663.06       $732.1527   $732.17   $732.15   $732.20