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 $156.35   3.833%   $162.3429   $162.34   $162.35   $162.30  
  Purchase #2 $17.31   5.162%   $18.2035   $18.20   $18.20   $18.20  
  Purchase #3 $26.56   3.698%   $27.5422   $27.54   $27.55   $27.50  
  Purchase #4 $114.41   10.856%   $126.8303   $126.83   $126.85   $126.80  
  Purchase #5 $26.51   3.855%   $27.532   $27.53   $27.55   $27.50  
  Purchase #6 $196.72   3.338%   $203.2865   $203.29   $203.30   $203.30  
  Purchase #7 $154.37   13.758%   $175.6082   $175.61   $175.60   $175.60  
  7 purchase totals = $692.23       $741.3456   $741.34   $741.40   $741.20