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 $238.41   9.577%   $261.2425   $261.24   $261.25   $261.20  
  Purchase #2 $152.91   7.171%   $163.8752   $163.88   $163.90   $163.90  
  Purchase #3 $23.89   10.121%   $26.3079   $26.31   $26.30   $26.30  
  Purchase #4 $215.40   8.163%   $232.9831   $232.98   $233.00   $233.00  
  Purchase #5 $118.49   12.183%   $132.9256   $132.93   $132.95   $132.90  
  Purchase #6 $154.44   13.163%   $174.7689   $174.77   $174.75   $174.80  
  Purchase #7 $128.82   7.344%   $138.2805   $138.28   $138.30   $138.30  
  7 purchase totals = $1,032.36       $1,130.3837   $1,130.39   $1,130.45   $1,130.40