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 $126.54   10.520%   $139.852   $139.85   $139.85   $139.90  
  Purchase #2 $108.65   5.210%   $114.3107   $114.31   $114.30   $114.30  
  Purchase #3 $248.77   6.120%   $263.9947   $263.99   $264.00   $264.00  
  Purchase #4 $243.42   11.610%   $271.6811   $271.68   $271.70   $271.70  
  Purchase #5 $38.29   5.339%   $40.3343   $40.33   $40.35   $40.30  
  Purchase #6 $228.47   12.667%   $257.4103   $257.41   $257.40   $257.40  
  Purchase #7 $248.45   11.279%   $276.4727   $276.47   $276.45   $276.50  
  7 purchase totals = $1,242.59       $1,364.0558   $1,364.04   $1,364.05   $1,364.10