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	$104.83	5.310%	$110.3965	$110.40	$110.40	$110.40
Purchase #2	$238.31	6.496%	$253.7906	$253.79	$253.80	$253.80
Purchase #3	$144.57	4.336%	$150.8386	$150.84	$150.85	$150.80
Purchase #4	$113.27	8.421%	$122.8085	$122.81	$122.80	$122.80
Purchase #5	$90.91	4.560%	$95.0555	$95.06	$95.05	$95.10
Purchase #6	$39.88	6.584%	$42.5057	$42.51	$42.50	$42.50
Purchase #7	$101.58	9.607%	$111.3388	$111.34	$111.35	$111.30
7 purchase totals =	$833.35		$886.7342	$886.75	$886.75	$886.70