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	$49.79	13.482%	$56.5027	$56.50	$56.50	$56.50
Purchase #2	$124.78	3.650%	$129.3345	$129.33	$129.35	$129.30
Purchase #3	$142.73	10.320%	$157.4597	$157.46	$157.45	$157.50
Purchase #4	$194.93	8.828%	$212.1384	$212.14	$212.15	$212.10
Purchase #5	$182.86	7.223%	$196.068	$196.07	$196.05	$196.10
Purchase #6	$124.83	11.463%	$139.1393	$139.14	$139.15	$139.10
Purchase #7	$229.96	5.435%	$242.4583	$242.46	$242.45	$242.50
7 purchase totals =	$1,049.88		$1,133.1009	$1,133.10	$1,133.10	$1,133.10