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	$85.63	5.164%	$90.0519	$90.05	$90.05	$90.10
Purchase #2	$76.60	9.820%	$84.1221	$84.12	$84.10	$84.10
Purchase #3	$148.40	8.139%	$160.4783	$160.48	$160.50	$160.50
Purchase #4	$76.34	13.324%	$86.5115	$86.51	$86.50	$86.50
Purchase #5	$215.31	12.430%	$242.073	$242.07	$242.05	$242.10
Purchase #6	$72.40	7.121%	$77.5556	$77.56	$77.55	$77.60
Purchase #7	$166.57	4.169%	$173.5143	$173.51	$173.50	$173.50
7 purchase totals =	$841.25		$914.3067	$914.30	$914.25	$914.40