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	$243.45	5.122%	$255.9195	$255.92	$255.90	$255.90
Purchase #2	$120.58	6.295%	$128.1705	$128.17	$128.15	$128.20
Purchase #3	$221.61	7.372%	$237.9471	$237.95	$237.95	$237.90
Purchase #4	$84.69	4.589%	$88.5764	$88.58	$88.60	$88.60
Purchase #5	$45.33	9.763%	$49.7556	$49.76	$49.75	$49.80
Purchase #6	$159.73	5.446%	$168.4289	$168.43	$168.45	$168.40
Purchase #7	$209.45	13.674%	$238.0902	$238.09	$238.10	$238.10
7 purchase totals =	$1,084.84		$1,166.8882	$1,166.90	$1,166.90	$1,166.90