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 $168.68   4.476%   $176.2301   $176.23   $176.25   $176.20  
  Purchase #2 $16.72   9.861%   $18.3688   $18.37   $18.35   $18.40  
  Purchase #3 $211.92   8.104%   $229.094   $229.09   $229.10   $229.10  
  Purchase #4 $15.42   10.653%   $17.0627   $17.06   $17.05   $17.10  
  Purchase #5 $239.80   9.336%   $262.1877   $262.19   $262.20   $262.20  
  Purchase #6 $195.70   8.759%   $212.8414   $212.84   $212.85   $212.80  
  Purchase #7 $58.83   11.652%   $65.6849   $65.68   $65.70   $65.70  
  7 purchase totals = $907.07       $981.4696   $981.46   $981.50   $981.50