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	$73.75	12.399%	$82.8943	$82.89	$82.90	$82.90
Purchase #2	$137.71	3.606%	$142.6758	$142.68	$142.70	$142.70
Purchase #3	$30.84	9.809%	$33.8651	$33.87	$33.85	$33.90
Purchase #4	$196.96	13.764%	$224.0696	$224.07	$224.05	$224.10
Purchase #5	$96.78	9.251%	$105.7331	$105.73	$105.75	$105.70
Purchase #6	$40.68	13.269%	$46.0778	$46.08	$46.10	$46.10
Purchase #7	$48.50	12.230%	$54.4316	$54.43	$54.45	$54.40
7 purchase totals =	$625.22		$689.7473	$689.75	$689.80	$689.80