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 $245.40   8.596%   $266.4946   $266.49   $266.50   $266.50  
  Purchase #2 $215.55   6.686%   $229.9617   $229.96   $229.95   $230.00  
  Purchase #3 $232.69   9.688%   $255.233   $255.23   $255.25   $255.20  
  Purchase #4 $157.84   9.307%   $172.5302   $172.53   $172.55   $172.50  
  Purchase #5 $236.31   13.121%   $267.3162   $267.32   $267.30   $267.30  
  Purchase #6 $54.45   11.398%   $60.6562   $60.66   $60.65   $60.70  
  Purchase #7 $186.44   5.766%   $197.1901   $197.19   $197.20   $197.20  
  7 purchase totals = $1,328.68       $1,449.3820   $1,449.38   $1,449.40   $1,449.40