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 $92.44   6.258%   $98.2249   $98.22   $98.20   $98.20  
  Purchase #2 $241.97   6.262%   $257.1222   $257.12   $257.10   $257.10  
  Purchase #3 $200.34   3.835%   $208.023   $208.02   $208.00   $208.00  
  Purchase #4 $59.70   6.768%   $63.7405   $63.74   $63.75   $63.70  
  Purchase #5 $232.50   10.809%   $257.6309   $257.63   $257.65   $257.60  
  Purchase #6 $65.77   6.632%   $70.1319   $70.13   $70.15   $70.10  
  Purchase #7 $71.88   9.318%   $78.5778   $78.58   $78.60   $78.60  
  7 purchase totals = $964.60       $1,033.4512   $1,033.44   $1,033.45   $1,033.30