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 $60.65   6.293%   $64.4667   $64.47   $64.45   $64.50  
  Purchase #2 $110.81   3.245%   $114.4058   $114.41   $114.40   $114.40  
  Purchase #3 $236.49   9.518%   $258.9991   $259.00   $259.00   $259.00  
  Purchase #4 $62.78   3.285%   $64.8423   $64.84   $64.85   $64.80  
  Purchase #5 $193.86   12.675%   $218.4318   $218.43   $218.45   $218.40  
  Purchase #6 $156.82   3.444%   $162.2209   $162.22   $162.20   $162.20  
  Purchase #7 $31.53   6.173%   $33.4763   $33.48   $33.50   $33.50  
  7 purchase totals = $852.94       $916.8429   $916.85   $916.85   $916.80