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	$36.50	12.133%	$40.9285	$40.93	$40.95	$40.90
Purchase #2	$248.30	8.472%	$269.336	$269.34	$269.35	$269.30
Purchase #3	$72.25	13.753%	$82.1865	$82.19	$82.20	$82.20
Purchase #4	$133.63	4.485%	$139.6233	$139.62	$139.60	$139.60
Purchase #5	$173.74	9.364%	$190.009	$190.01	$190.00	$190.00
Purchase #6	$117.43	11.360%	$130.77	$130.77	$130.75	$130.80
Purchase #7	$209.72	8.769%	$228.1103	$228.11	$228.10	$228.10
7 purchase totals =	$991.57		$1,080.9636	$1,080.97	$1,080.95	$1,080.90