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 $236.86   4.589%   $247.7295   $247.73   $247.75   $247.70  
  Purchase #2 $181.59   7.144%   $194.5628   $194.56   $194.55   $194.60  
  Purchase #3 $154.78   6.130%   $164.268   $164.27   $164.25   $164.30  
  Purchase #4 $101.89   13.335%   $115.477   $115.48   $115.50   $115.50  
  Purchase #5 $211.74   4.284%   $220.8109   $220.81   $220.80   $220.80  
  Purchase #6 $14.55   8.377%   $15.7689   $15.77   $15.75   $15.80  
  Purchase #7 $54.87   10.744%   $60.7652   $60.77   $60.75   $60.80  
  7 purchase totals = $956.28       $1,019.3823   $1,019.39   $1,019.35   $1,019.50