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 $222.66   6.549%   $237.242   $237.24   $237.25   $237.20  
  Purchase #2 $38.47   5.794%   $40.699   $40.70   $40.70   $40.70  
  Purchase #3 $12.54   8.315%   $13.5827   $13.58   $13.60   $13.60  
  Purchase #4 $211.25   13.818%   $240.4405   $240.44   $240.45   $240.40  
  Purchase #5 $205.49   10.441%   $226.9452   $226.95   $226.95   $226.90  
  Purchase #6 $142.50   11.716%   $159.1953   $159.20   $159.20   $159.20  
  Purchase #7 $125.81   6.772%   $134.3299   $134.33   $134.35   $134.30  
  7 purchase totals = $958.72       $1,052.4346   $1,052.44   $1,052.50   $1,052.30