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	$88.66	13.169%	$100.3356	$100.34	$100.35	$100.30
Purchase #2	$214.56	10.611%	$237.327	$237.33	$237.35	$237.30
Purchase #3	$98.25	8.614%	$106.7133	$106.71	$106.70	$106.70
Purchase #4	$130.88	5.150%	$137.6203	$137.62	$137.60	$137.60
Purchase #5	$231.31	4.428%	$241.5524	$241.55	$241.55	$241.60
Purchase #6	$175.94	11.595%	$196.3402	$196.34	$196.35	$196.30
Purchase #7	$42.77	9.267%	$46.7335	$46.73	$46.75	$46.70
7 purchase totals =	$982.37		$1,066.6223	$1,066.62	$1,066.65	$1,066.50