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	$147.36	8.400%	$159.7382	$159.74	$159.75	$159.70
Purchase #2	$122.25	3.130%	$126.0764	$126.08	$126.10	$126.10
Purchase #3	$114.88	7.596%	$123.6063	$123.61	$123.60	$123.60
Purchase #4	$226.80	12.164%	$254.388	$254.39	$254.40	$254.40
Purchase #5	$28.60	12.417%	$32.1513	$32.15	$32.15	$32.20
Purchase #6	$210.71	7.223%	$225.9296	$225.93	$225.95	$225.90
Purchase #7	$72.53	12.313%	$81.4606	$81.46	$81.45	$81.50
7 purchase totals =	$923.13		$1,003.3504	$1,003.36	$1,003.40	$1,003.40