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 $173.41   11.827%   $193.9192   $193.92   $193.90   $193.90  
  Purchase #2 $38.73   13.181%   $43.835   $43.84   $43.85   $43.80  
  Purchase #3 $180.90   9.232%   $197.6007   $197.60   $197.60   $197.60  
  Purchase #4 $33.45   12.467%   $37.6202   $37.62   $37.60   $37.60  
  Purchase #5 $113.99   10.802%   $126.3032   $126.30   $126.30   $126.30  
  Purchase #6 $212.71   12.592%   $239.4944   $239.49   $239.50   $239.50  
  Purchase #7 $216.40   6.209%   $229.8363   $229.84   $229.85   $229.80  
  7 purchase totals = $969.59       $1,068.6090   $1,068.61   $1,068.60   $1,068.50