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	$183.92	11.170%	$204.4639	$204.46	$204.45	$204.50
Purchase #2	$91.43	8.854%	$99.5252	$99.53	$99.55	$99.50
Purchase #3	$9.90	6.447%	$10.5383	$10.54	$10.55	$10.50
Purchase #4	$168.61	6.788%	$180.0552	$180.06	$180.05	$180.10
Purchase #5	$93.31	11.588%	$104.1228	$104.12	$104.10	$104.10
Purchase #6	$213.45	13.563%	$242.4002	$242.40	$242.40	$242.40
Purchase #7	$127.96	4.274%	$133.429	$133.43	$133.45	$133.40
7 purchase totals =	$888.58		$974.5346	$974.54	$974.55	$974.50