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 $216.33   10.747%   $239.579   $239.58   $239.60   $239.60  
  Purchase #2 $59.83   8.164%   $64.7145   $64.71   $64.70   $64.70  
  Purchase #3 $225.57   3.285%   $232.98   $232.98   $233.00   $233.00  
  Purchase #4 $247.96   9.709%   $272.0344   $272.03   $272.05   $272.00  
  Purchase #5 $23.29   12.341%   $26.1642   $26.16   $26.15   $26.20  
  Purchase #6 $107.62   8.473%   $116.7386   $116.74   $116.75   $116.70  
  Purchase #7 $27.40   10.709%   $30.3343   $30.33   $30.35   $30.30  
  7 purchase totals = $908.00       $982.5450   $982.53   $982.60   $982.50