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	$79.47	11.569%	$88.6639	$88.66	$88.65	$88.70
Purchase #2	$187.76	4.710%	$196.6035	$196.60	$196.60	$196.60
Purchase #3	$226.39	3.502%	$234.3182	$234.32	$234.30	$234.30
Purchase #4	$53.78	10.247%	$59.2908	$59.29	$59.30	$59.30
Purchase #5	$225.59	3.369%	$233.1901	$233.19	$233.20	$233.20
Purchase #6	$219.60	12.684%	$247.4541	$247.45	$247.45	$247.50
Purchase #7	$135.53	12.375%	$152.3018	$152.30	$152.30	$152.30
7 purchase totals =	$1,128.12		$1,211.8224	$1,211.81	$1,211.80	$1,211.90