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	$100.89	8.841%	$109.8097	$109.81	$109.80	$109.80
Purchase #2	$187.50	10.362%	$206.9288	$206.93	$206.95	$206.90
Purchase #3	$212.73	8.311%	$230.41	$230.41	$230.40	$230.40
Purchase #4	$42.60	7.340%	$45.7268	$45.73	$45.75	$45.70
Purchase #5	$141.39	8.248%	$153.0518	$153.05	$153.05	$153.10
Purchase #6	$82.64	4.650%	$86.4828	$86.48	$86.50	$86.50
Purchase #7	$70.65	4.574%	$73.8815	$73.88	$73.90	$73.90
7 purchase totals =	$838.40		$906.2914	$906.29	$906.35	$906.30