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 $60.97   12.460%   $68.5669   $68.57   $68.55   $68.60  
  Purchase #2 $191.45   13.381%   $217.0679   $217.07   $217.05   $217.10  
  Purchase #3 $104.37   9.782%   $114.5795   $114.58   $114.60   $114.60  
  Purchase #4 $35.85   3.205%   $36.999   $37.00   $37.00   $37.00  
  Purchase #5 $15.90   4.709%   $16.6487   $16.65   $16.65   $16.60  
  Purchase #6 $201.58   6.600%   $214.8843   $214.88   $214.90   $214.90  
  Purchase #7 $219.60   7.495%   $236.059   $236.06   $236.05   $236.10  
  7 purchase totals = $829.72       $904.8053   $904.81   $904.80   $904.90