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	$92.68	12.794%	$104.5375	$104.54	$104.55	$104.50
Purchase #2	$120.88	8.569%	$131.2382	$131.24	$131.25	$131.20
Purchase #3	$160.37	11.871%	$179.4075	$179.41	$179.40	$179.40
Purchase #4	$63.82	11.872%	$71.3967	$71.40	$71.40	$71.40
Purchase #5	$191.67	11.400%	$213.5204	$213.52	$213.50	$213.50
Purchase #6	$85.66	11.103%	$95.1708	$95.17	$95.15	$95.20
Purchase #7	$57.40	4.719%	$60.1087	$60.11	$60.10	$60.10
7 purchase totals =	$772.48		$855.3798	$855.39	$855.35	$855.30