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 $69.98   8.207%   $75.7233   $75.72   $75.70   $75.70  
  Purchase #2 $68.59   8.458%   $74.3913   $74.39   $74.40   $74.40  
  Purchase #3 $79.94   10.686%   $88.4824   $88.48   $88.50   $88.50  
  Purchase #4 $114.93   3.602%   $119.0698   $119.07   $119.05   $119.10  
  Purchase #5 $132.30   10.507%   $146.2008   $146.20   $146.20   $146.20  
  Purchase #6 $62.97   10.397%   $69.517   $69.52   $69.50   $69.50  
  Purchase #7 $162.62   12.595%   $183.102   $183.10   $183.10   $183.10  
  7 purchase totals = $691.33       $756.4866   $756.48   $756.45   $756.50