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	$77.64	7.143%	$83.1858	$83.19	$83.20	$83.20
Purchase #2	$39.74	7.589%	$42.7559	$42.76	$42.75	$42.80
Purchase #3	$140.40	3.869%	$145.8321	$145.83	$145.85	$145.80
Purchase #4	$92.91	10.238%	$102.4221	$102.42	$102.40	$102.40
Purchase #5	$167.49	13.770%	$190.5534	$190.55	$190.55	$190.60
Purchase #6	$155.41	10.212%	$171.2805	$171.28	$171.30	$171.30
Purchase #7	$141.46	13.301%	$160.2756	$160.28	$160.30	$160.30
7 purchase totals =	$815.05		$896.3054	$896.31	$896.35	$896.40