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	$159.53	7.822%	$172.0084	$172.01	$172.00	$172.00
Purchase #2	$79.64	8.546%	$86.446	$86.45	$86.45	$86.40
Purchase #3	$144.40	3.813%	$149.906	$149.91	$149.90	$149.90
Purchase #4	$197.30	6.430%	$209.9864	$209.99	$210.00	$210.00
Purchase #5	$185.29	6.560%	$197.445	$197.45	$197.45	$197.40
Purchase #6	$80.37	12.169%	$90.1502	$90.15	$90.15	$90.20
Purchase #7	$82.86	8.530%	$89.928	$89.93	$89.95	$89.90
7 purchase totals =	$929.39		$995.8700	$995.89	$995.90	$995.80