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	$101.88	7.275%	$109.2918	$109.29	$109.30	$109.30
Purchase #2	$72.65	6.716%	$77.5292	$77.53	$77.55	$77.50
Purchase #3	$209.56	7.401%	$225.0695	$225.07	$225.05	$225.10
Purchase #4	$154.43	13.128%	$174.7036	$174.70	$174.70	$174.70
Purchase #5	$47.61	9.751%	$52.2525	$52.25	$52.25	$52.30
Purchase #6	$60.82	10.673%	$67.3113	$67.31	$67.30	$67.30
Purchase #7	$85.55	3.351%	$88.4168	$88.42	$88.40	$88.40
7 purchase totals =	$732.50		$794.5747	$794.57	$794.55	$794.60