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	$10.70	11.322%	$11.9115	$11.91	$11.90	$11.90
Purchase #2	$211.89	7.407%	$227.5847	$227.58	$227.60	$227.60
Purchase #3	$86.55	8.664%	$94.0487	$94.05	$94.05	$94.00
Purchase #4	$244.56	13.512%	$277.6049	$277.60	$277.60	$277.60
Purchase #5	$79.31	4.134%	$82.5887	$82.59	$82.60	$82.60
Purchase #6	$10.65	7.821%	$11.4829	$11.48	$11.50	$11.50
Purchase #7	$236.31	8.116%	$255.4889	$255.49	$255.50	$255.50
7 purchase totals =	$879.97		$960.7103	$960.70	$960.75	$960.70