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 $114.73   8.366%   $124.3283   $124.33   $124.35   $124.30  
  Purchase #2 $139.93   9.104%   $152.6692   $152.67   $152.65   $152.70  
  Purchase #3 $27.51   11.168%   $30.5823   $30.58   $30.60   $30.60  
  Purchase #4 $78.99   13.633%   $89.7587   $89.76   $89.75   $89.80  
  Purchase #5 $43.87   5.263%   $46.1789   $46.18   $46.20   $46.20  
  Purchase #6 $7.87   8.740%   $8.5578   $8.56   $8.55   $8.60  
  Purchase #7 $153.64   3.811%   $159.4952   $159.50   $159.50   $159.50  
  7 purchase totals = $566.54       $611.5704   $611.58   $611.60   $611.70