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 $61.71   13.547%   $70.0699   $70.07   $70.05   $70.10  
  Purchase #2 $127.29   5.506%   $134.2986   $134.30   $134.30   $134.30  
  Purchase #3 $162.49   13.469%   $184.3758   $184.38   $184.40   $184.40  
  Purchase #4 $15.63   4.487%   $16.3313   $16.33   $16.35   $16.30  
  Purchase #5 $95.30   3.471%   $98.6079   $98.61   $98.60   $98.60  
  Purchase #6 $78.97   3.802%   $81.9724   $81.97   $81.95   $82.00  
  Purchase #7 $154.63   3.807%   $160.5168   $160.52   $160.50   $160.50  
  7 purchase totals = $696.02       $746.1727   $746.18   $746.15   $746.20