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	$78.54	8.843%	$85.4853	$85.49	$85.50	$85.50
Purchase #2	$93.55	12.623%	$105.3588	$105.36	$105.35	$105.40
Purchase #3	$161.34	11.484%	$179.8683	$179.87	$179.85	$179.90
Purchase #4	$78.38	3.263%	$80.9375	$80.94	$80.95	$80.90
Purchase #5	$149.39	5.536%	$157.6602	$157.66	$157.65	$157.70
Purchase #6	$131.89	13.293%	$149.4221	$149.42	$149.40	$149.40
Purchase #7	$207.86	5.557%	$219.4108	$219.41	$219.40	$219.40
7 purchase totals =	$900.95		$978.1430	$978.15	$978.10	$978.20