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	$100.30	3.141%	$103.4504	$103.45	$103.45	$103.50
Purchase #2	$108.93	10.639%	$120.5191	$120.52	$120.50	$120.50
Purchase #3	$148.50	11.214%	$165.1528	$165.15	$165.15	$165.20
Purchase #4	$37.72	7.401%	$40.5117	$40.51	$40.50	$40.50
Purchase #5	$105.86	13.367%	$120.0103	$120.01	$120.00	$120.00
Purchase #6	$135.56	10.263%	$149.4725	$149.47	$149.45	$149.50
Purchase #7	$144.54	8.658%	$157.0543	$157.05	$157.05	$157.10
7 purchase totals =	$781.41		$856.1711	$856.16	$856.10	$856.30