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	$87.71	4.116%	$91.3201	$91.32	$91.30	$91.30
Purchase #2	$11.73	12.794%	$13.2307	$13.23	$13.25	$13.20
Purchase #3	$50.83	8.473%	$55.1368	$55.14	$55.15	$55.10
Purchase #4	$103.53	12.234%	$116.1959	$116.20	$116.20	$116.20
Purchase #5	$97.94	8.105%	$105.878	$105.88	$105.90	$105.90
Purchase #6	$36.52	6.312%	$38.8251	$38.83	$38.85	$38.80
Purchase #7	$48.64	13.750%	$55.328	$55.33	$55.35	$55.30
7 purchase totals =	$436.90		$475.9146	$475.93	$476.00	$475.80