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	$92.84	8.689%	$100.9069	$100.91	$100.90	$100.90
Purchase #2	$241.39	12.810%	$272.3121	$272.31	$272.30	$272.30
Purchase #3	$25.72	9.680%	$28.2097	$28.21	$28.20	$28.20
Purchase #4	$245.93	13.229%	$278.4641	$278.46	$278.45	$278.50
Purchase #5	$68.80	8.860%	$74.8957	$74.90	$74.90	$74.90
Purchase #6	$248.74	10.689%	$275.3278	$275.33	$275.35	$275.30
Purchase #7	$99.43	10.729%	$110.0978	$110.10	$110.10	$110.10
7 purchase totals =	$1,022.85		$1,140.2141	$1,140.22	$1,140.20	$1,140.20