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 $149.89   7.856%   $161.6654   $161.67   $161.65   $161.70  
  Purchase #2 $185.28   5.501%   $195.4723   $195.47   $195.45   $195.50  
  Purchase #3 $113.46   4.619%   $118.7007   $118.70   $118.70   $118.70  
  Purchase #4 $82.69   4.845%   $86.6963   $86.70   $86.70   $86.70  
  Purchase #5 $22.89   10.779%   $25.3573   $25.36   $25.35   $25.40  
  Purchase #6 $164.48   13.171%   $186.1437   $186.14   $186.15   $186.10  
  Purchase #7 $35.50   4.735%   $37.1809   $37.18   $37.20   $37.20  
  7 purchase totals = $754.19       $811.2166   $811.22   $811.20   $811.30