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 $166.49   5.804%   $176.1531   $176.15   $176.15   $176.20  
  Purchase #2 $106.49   12.311%   $119.6   $119.60   $119.60   $119.60  
  Purchase #3 $72.47   5.245%   $76.2711   $76.27   $76.25   $76.30  
  Purchase #4 $58.46   5.574%   $61.7186   $61.72   $61.70   $61.70  
  Purchase #5 $41.28   6.776%   $44.0771   $44.08   $44.10   $44.10  
  Purchase #6 $236.48   11.562%   $263.8218   $263.82   $263.80   $263.80  
  Purchase #7 $124.34   13.312%   $140.8921   $140.89   $140.90   $140.90  
  7 purchase totals = $806.01       $882.5338   $882.53   $882.50   $882.60