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	$40.79	4.805%	$42.75	$42.75	$42.75	$42.80
Purchase #2	$110.31	8.865%	$120.089	$120.09	$120.10	$120.10
Purchase #3	$40.91	11.248%	$45.5116	$45.51	$45.50	$45.50
Purchase #4	$167.45	13.145%	$189.4613	$189.46	$189.45	$189.50
Purchase #5	$103.94	7.309%	$111.537	$111.54	$111.55	$111.50
Purchase #6	$232.86	13.144%	$263.4671	$263.47	$263.45	$263.50
Purchase #7	$197.29	5.257%	$207.6615	$207.66	$207.65	$207.70
7 purchase totals =	$893.55		$980.4775	$980.48	$980.45	$980.60