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	$83.72	6.531%	$89.1878	$89.19	$89.20	$89.20
Purchase #2	$159.83	10.531%	$176.6617	$176.66	$176.65	$176.70
Purchase #3	$220.47	3.219%	$227.5669	$227.57	$227.55	$227.60
Purchase #4	$198.52	12.542%	$223.4184	$223.42	$223.40	$223.40
Purchase #5	$40.65	12.262%	$45.6345	$45.63	$45.65	$45.60
Purchase #6	$135.50	5.508%	$142.9633	$142.96	$142.95	$143.00
Purchase #7	$226.47	4.518%	$236.7019	$236.70	$236.70	$236.70
7 purchase totals =	$1,065.16		$1,142.1345	$1,142.13	$1,142.10	$1,142.20