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	$80.35	13.846%	$91.4753	$91.48	$91.50	$91.50
Purchase #2	$146.83	12.673%	$165.4378	$165.44	$165.45	$165.40
Purchase #3	$169.97	12.623%	$191.4253	$191.43	$191.45	$191.40
Purchase #4	$117.66	3.170%	$121.3898	$121.39	$121.40	$121.40
Purchase #5	$18.29	8.818%	$19.9028	$19.90	$19.90	$19.90
Purchase #6	$128.37	12.229%	$144.0684	$144.07	$144.05	$144.10
Purchase #7	$111.84	3.621%	$115.8897	$115.89	$115.90	$115.90
7 purchase totals =	$773.31		$849.5891	$849.60	$849.65	$849.60