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	$99.58	9.781%	$109.3199	$109.32	$109.30	$109.30
Purchase #2	$43.40	10.849%	$48.1085	$48.11	$48.10	$48.10
Purchase #3	$10.43	3.822%	$10.8286	$10.83	$10.85	$10.80
Purchase #4	$42.50	4.433%	$44.384	$44.38	$44.40	$44.40
Purchase #5	$189.26	11.839%	$211.6665	$211.67	$211.65	$211.70
Purchase #6	$245.30	11.311%	$273.0459	$273.05	$273.05	$273.00
Purchase #7	$103.71	13.850%	$118.0738	$118.07	$118.05	$118.10
7 purchase totals =	$734.18		$815.4272	$815.43	$815.40	$815.40