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 $34.45   4.164%   $35.8845   $35.88   $35.90   $35.90  
  Purchase #2 $211.74   13.185%   $239.6579   $239.66   $239.65   $239.70  
  Purchase #3 $148.95   3.403%   $154.0188   $154.02   $154.00   $154.00  
  Purchase #4 $15.63   3.452%   $16.1695   $16.17   $16.15   $16.20  
  Purchase #5 $184.88   12.419%   $207.8402   $207.84   $207.85   $207.80  
  Purchase #6 $246.95   8.848%   $268.8001   $268.80   $268.80   $268.80  
  Purchase #7 $162.25   12.500%   $182.5313   $182.53   $182.55   $182.50  
  7 purchase totals = $1,004.85       $1,104.9023   $1,104.90   $1,104.90   $1,104.90