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	$90.94	12.714%	$102.5021	$102.50	$102.50	$102.50
Purchase #2	$179.57	10.684%	$198.7553	$198.76	$198.75	$198.80
Purchase #3	$184.97	8.396%	$200.5001	$200.50	$200.50	$200.50
Purchase #4	$54.38	6.826%	$58.092	$58.09	$58.10	$58.10
Purchase #5	$179.31	9.755%	$196.8017	$196.80	$196.80	$196.80
Purchase #6	$215.58	7.796%	$232.3866	$232.39	$232.40	$232.40
Purchase #7	$200.58	13.209%	$227.0746	$227.07	$227.05	$227.10
7 purchase totals =	$1,105.33		$1,216.1124	$1,216.11	$1,216.10	$1,216.20