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 $235.26   3.858%   $244.3363   $244.34   $244.35   $244.30  
  Purchase #2 $168.77   6.598%   $179.9054   $179.91   $179.90   $179.90  
  Purchase #3 $208.82   12.857%   $235.668   $235.67   $235.65   $235.70  
  Purchase #4 $165.35   6.483%   $176.0696   $176.07   $176.05   $176.10  
  Purchase #5 $106.69   13.828%   $121.4431   $121.44   $121.45   $121.40  
  Purchase #6 $59.27   8.346%   $64.2167   $64.22   $64.20   $64.20  
  Purchase #7 $195.78   6.152%   $207.8244   $207.82   $207.80   $207.80  
  7 purchase totals = $1,139.94       $1,229.4635   $1,229.47   $1,229.40   $1,229.40