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	$9.56	4.557%	$9.9956	$10.00	$10.00	$10.00
Purchase #2	$86.47	3.428%	$89.4342	$89.43	$89.45	$89.40
Purchase #3	$14.72	13.524%	$16.7107	$16.71	$16.70	$16.70
Purchase #4	$43.56	4.325%	$45.444	$45.44	$45.45	$45.40
Purchase #5	$130.47	7.339%	$140.0452	$140.05	$140.05	$140.00
Purchase #6	$181.50	10.111%	$199.8515	$199.85	$199.85	$199.90
Purchase #7	$28.60	13.318%	$32.4089	$32.41	$32.40	$32.40
7 purchase totals =	$494.88		$533.8901	$533.89	$533.90	$533.80