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 $165.88   10.491%   $183.2825   $183.28   $183.30   $183.30  
  Purchase #2 $250.62   4.437%   $261.74   $261.74   $261.75   $261.70  
  Purchase #3 $35.41   4.673%   $37.0647   $37.06   $37.05   $37.10  
  Purchase #4 $84.56   11.722%   $94.4721   $94.47   $94.45   $94.50  
  Purchase #5 $221.53   3.326%   $228.8981   $228.90   $228.90   $228.90  
  Purchase #6 $212.60   13.748%   $241.8282   $241.83   $241.85   $241.80  
  Purchase #7 $22.65   10.554%   $25.0405   $25.04   $25.05   $25.00  
  7 purchase totals = $993.25       $1,072.3261   $1,072.32   $1,072.35   $1,072.30