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 $209.45   6.119%   $222.2662   $222.27   $222.25   $222.30  
  Purchase #2 $201.66   11.347%   $224.5424   $224.54   $224.55   $224.50  
  Purchase #3 $137.63   10.582%   $152.194   $152.19   $152.20   $152.20  
  Purchase #4 $231.66   3.299%   $239.3025   $239.30   $239.30   $239.30  
  Purchase #5 $183.67   8.548%   $199.3701   $199.37   $199.35   $199.40  
  Purchase #6 $81.96   12.232%   $91.9853   $91.99   $92.00   $92.00  
  Purchase #7 $114.71   5.147%   $120.6141   $120.61   $120.60   $120.60  
  7 purchase totals = $1,160.74       $1,250.2746   $1,250.27   $1,250.25   $1,250.30