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	$44.28	13.271%	$50.1564	$50.16	$50.15	$50.20
Purchase #2	$157.46	5.755%	$166.5218	$166.52	$166.50	$166.50
Purchase #3	$110.73	6.550%	$117.9828	$117.98	$118.00	$118.00
Purchase #4	$109.89	12.658%	$123.7999	$123.80	$123.80	$123.80
Purchase #5	$233.43	8.627%	$253.568	$253.57	$253.55	$253.60
Purchase #6	$75.48	3.660%	$78.2426	$78.24	$78.25	$78.20
Purchase #7	$250.38	13.450%	$284.0561	$284.06	$284.05	$284.10
7 purchase totals =	$981.65		$1,074.3276	$1,074.33	$1,074.30	$1,074.40