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 $49.69   13.196%   $56.2471   $56.25   $56.25   $56.20  
  Purchase #2 $104.27   5.770%   $110.2864   $110.29   $110.30   $110.30  
  Purchase #3 $163.60   8.537%   $177.5665   $177.57   $177.55   $177.60  
  Purchase #4 $163.78   5.581%   $172.9206   $172.92   $172.90   $172.90  
  Purchase #5 $249.46   4.449%   $260.5585   $260.56   $260.55   $260.60  
  Purchase #6 $108.35   9.463%   $118.6032   $118.60   $118.60   $118.60  
  Purchase #7 $248.26   12.148%   $278.4186   $278.42   $278.40   $278.40  
  7 purchase totals = $1,087.41       $1,174.6009   $1,174.61   $1,174.55   $1,174.60