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 $71.48   6.819%   $76.3542   $76.35   $76.35   $76.40  
  Purchase #2 $177.72   3.723%   $184.3365   $184.34   $184.35   $184.30  
  Purchase #3 $21.27   9.141%   $23.2143   $23.21   $23.20   $23.20  
  Purchase #4 $61.42   6.714%   $65.5437   $65.54   $65.55   $65.50  
  Purchase #5 $223.87   11.757%   $250.1904   $250.19   $250.20   $250.20  
  Purchase #6 $72.54   3.474%   $75.06   $75.06   $75.05   $75.10  
  Purchase #7 $55.97   5.617%   $59.1138   $59.11   $59.10   $59.10  
  7 purchase totals = $684.27       $733.8129   $733.80   $733.80   $733.80