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 $49.71   13.649%   $56.4949   $56.49   $56.50   $56.50  
  Purchase #2 $231.57   4.748%   $242.5649   $242.56   $242.55   $242.60  
  Purchase #3 $162.62   4.755%   $170.3526   $170.35   $170.35   $170.40  
  Purchase #4 $62.68   13.140%   $70.9162   $70.92   $70.90   $70.90  
  Purchase #5 $211.73   3.734%   $219.636   $219.64   $219.65   $219.60  
  Purchase #6 $93.63   9.856%   $102.8582   $102.86   $102.85   $102.90  
  Purchase #7 $131.76   8.236%   $142.6118   $142.61   $142.60   $142.60  
  7 purchase totals = $943.70       $1,005.4346   $1,005.43   $1,005.40   $1,005.50