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	$39.44	7.781%	$42.5088	$42.51	$42.50	$42.50
Purchase #2	$196.95	5.424%	$207.6326	$207.63	$207.65	$207.60
Purchase #3	$131.58	4.454%	$137.4406	$137.44	$137.45	$137.40
Purchase #4	$95.48	4.137%	$99.43	$99.43	$99.45	$99.40
Purchase #5	$167.26	13.304%	$189.5123	$189.51	$189.50	$189.50
Purchase #6	$87.31	11.566%	$97.4083	$97.41	$97.40	$97.40
Purchase #7	$138.45	11.501%	$154.3731	$154.37	$154.35	$154.40
7 purchase totals =	$856.47		$928.3057	$928.30	$928.30	$928.20