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 $59.51   6.237%   $63.2216   $63.22   $63.20   $63.20  
  Purchase #2 $42.46   5.129%   $44.6378   $44.64   $44.65   $44.60  
  Purchase #3 $101.39   3.176%   $104.6101   $104.61   $104.60   $104.60  
  Purchase #4 $232.59   11.478%   $259.2867   $259.29   $259.30   $259.30  
  Purchase #5 $114.30   12.684%   $128.7978   $128.80   $128.80   $128.80  
  Purchase #6 $192.30   11.865%   $215.1164   $215.12   $215.10   $215.10  
  Purchase #7 $214.94   7.422%   $230.8928   $230.89   $230.90   $230.90  
  7 purchase totals = $957.49       $1,046.5632   $1,046.57   $1,046.55   $1,046.50