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	$18.98	6.154%	$20.148	$20.15	$20.15	$20.10
Purchase #2	$188.81	8.460%	$204.7833	$204.78	$204.80	$204.80
Purchase #3	$91.87	9.590%	$100.6803	$100.68	$100.70	$100.70
Purchase #4	$30.57	8.123%	$33.0532	$33.05	$33.05	$33.10
Purchase #5	$167.75	13.500%	$190.3963	$190.40	$190.40	$190.40
Purchase #6	$42.97	8.756%	$46.7325	$46.73	$46.75	$46.70
Purchase #7	$37.35	8.655%	$40.5826	$40.58	$40.60	$40.60
7 purchase totals =	$578.30		$636.3762	$636.37	$636.45	$636.40