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 $52.73   11.315%   $58.6964   $58.70   $58.70   $58.70  
  Purchase #2 $178.41   5.621%   $188.4384   $188.44   $188.45   $188.40  
  Purchase #3 $6.99   3.158%   $7.2107   $7.21   $7.20   $7.20  
  Purchase #4 $27.68   4.307%   $28.8722   $28.87   $28.85   $28.90  
  Purchase #5 $216.37   9.768%   $237.505   $237.51   $237.50   $237.50  
  Purchase #6 $207.70   12.453%   $233.5649   $233.56   $233.55   $233.60  
  Purchase #7 $198.50   8.209%   $214.7949   $214.79   $214.80   $214.80  
  7 purchase totals = $888.38       $969.0825   $969.08   $969.05   $969.10