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 $174.94   11.659%   $195.3363   $195.34   $195.35   $195.30  
  Purchase #2 $230.68   12.314%   $259.0859   $259.09   $259.10   $259.10  
  Purchase #3 $211.88   11.508%   $236.2632   $236.26   $236.25   $236.30  
  Purchase #4 $101.47   10.380%   $112.0026   $112.00   $112.00   $112.00  
  Purchase #5 $63.93   7.833%   $68.9376   $68.94   $68.95   $68.90  
  Purchase #6 $209.88   5.210%   $220.8147   $220.81   $220.80   $220.80  
  Purchase #7 $126.98   3.325%   $131.2021   $131.20   $131.20   $131.20  
  7 purchase totals = $1,119.76       $1,223.6424   $1,223.64   $1,223.65   $1,223.60