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 $67.40   3.863%   $70.0037   $70.00   $70.00   $70.00  
  Purchase #2 $8.29   5.635%   $8.7571   $8.76   $8.75   $8.80  
  Purchase #3 $52.38   4.155%   $54.5564   $54.56   $54.55   $54.60  
  Purchase #4 $177.63   3.607%   $184.0371   $184.04   $184.05   $184.00  
  Purchase #5 $250.43   11.630%   $279.555   $279.56   $279.55   $279.60  
  Purchase #6 $82.64   4.384%   $86.2629   $86.26   $86.25   $86.30  
  Purchase #7 $68.91   7.606%   $74.1513   $74.15   $74.15   $74.20  
  7 purchase totals = $707.68       $757.3235   $757.33   $757.30   $757.50