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	$22.34	3.293%	$23.0757	$23.08	$23.10	$23.10
Purchase #2	$155.55	4.576%	$162.668	$162.67	$162.65	$162.70
Purchase #3	$212.52	8.188%	$229.9211	$229.92	$229.90	$229.90
Purchase #4	$44.29	3.760%	$45.9553	$45.96	$45.95	$46.00
Purchase #5	$73.94	6.318%	$78.6115	$78.61	$78.60	$78.60
Purchase #6	$82.96	7.591%	$89.2575	$89.26	$89.25	$89.30
Purchase #7	$11.33	11.824%	$12.6697	$12.67	$12.65	$12.70
7 purchase totals =	$602.93		$642.1588	$642.17	$642.10	$642.30