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	$237.38	3.170%	$244.9049	$244.90	$244.90	$244.90
Purchase #2	$80.92	9.417%	$88.5402	$88.54	$88.55	$88.50
Purchase #3	$167.56	3.301%	$173.0912	$173.09	$173.10	$173.10
Purchase #4	$55.57	12.460%	$62.494	$62.49	$62.50	$62.50
Purchase #5	$53.92	4.708%	$56.4586	$56.46	$56.45	$56.50
Purchase #6	$166.89	10.852%	$185.0009	$185.00	$185.00	$185.00
Purchase #7	$110.88	7.646%	$119.3579	$119.36	$119.35	$119.40
7 purchase totals =	$873.12		$929.8477	$929.84	$929.85	$929.90