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	$190.68	13.372%	$216.1777	$216.18	$216.20	$216.20
Purchase #2	$91.47	13.563%	$103.8761	$103.88	$103.90	$103.90
Purchase #3	$114.58	12.432%	$128.8246	$128.82	$128.80	$128.80
Purchase #4	$112.84	10.539%	$124.7322	$124.73	$124.75	$124.70
Purchase #5	$198.52	12.808%	$223.9464	$223.95	$223.95	$223.90
Purchase #6	$119.25	6.777%	$127.3316	$127.33	$127.35	$127.30
Purchase #7	$143.26	3.542%	$148.3343	$148.33	$148.35	$148.30
7 purchase totals =	$970.60		$1,073.2229	$1,073.22	$1,073.30	$1,073.10