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	$42.26	13.869%	$48.121	$48.12	$48.10	$48.10
Purchase #2	$183.81	9.243%	$200.7996	$200.80	$200.80	$200.80
Purchase #3	$57.31	3.720%	$59.4419	$59.44	$59.45	$59.40
Purchase #4	$84.83	5.118%	$89.1716	$89.17	$89.15	$89.20
Purchase #5	$51.57	6.131%	$54.7318	$54.73	$54.75	$54.70
Purchase #6	$208.90	4.357%	$218.0018	$218.00	$218.00	$218.00
Purchase #7	$62.76	4.350%	$65.4901	$65.49	$65.50	$65.50
7 purchase totals =	$691.44		$735.7578	$735.75	$735.75	$735.70