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 $174.87   5.820%   $185.0474   $185.05   $185.05   $185.00  
  Purchase #2 $63.41   4.394%   $66.1962   $66.20   $66.20   $66.20  
  Purchase #3 $113.65   3.544%   $117.6778   $117.68   $117.70   $117.70  
  Purchase #4 $74.53   5.501%   $78.6299   $78.63   $78.65   $78.60  
  Purchase #5 $139.30   5.624%   $147.1342   $147.13   $147.15   $147.10  
  Purchase #6 $97.34   9.658%   $106.7411   $106.74   $106.75   $106.70  
  Purchase #7 $118.91   4.294%   $124.016   $124.02   $124.00   $124.00  
  7 purchase totals = $782.01       $825.4426   $825.45   $825.50   $825.30