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 $246.53   9.272%   $269.3883   $269.39   $269.40   $269.40  
  Purchase #2 $23.35   5.388%   $24.6081   $24.61   $24.60   $24.60  
  Purchase #3 $165.34   5.343%   $174.1741   $174.17   $174.15   $174.20  
  Purchase #4 $35.54   12.420%   $39.9541   $39.95   $39.95   $40.00  
  Purchase #5 $45.97   13.528%   $52.1888   $52.19   $52.20   $52.20  
  Purchase #6 $142.72   9.345%   $156.0572   $156.06   $156.05   $156.10  
  Purchase #7 $218.38   12.767%   $246.2606   $246.26   $246.25   $246.30  
  7 purchase totals = $877.83       $962.6312   $962.63   $962.60   $962.80