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	$128.61	10.813%	$142.5166	$142.52	$142.50	$142.50
Purchase #2	$230.89	10.370%	$254.8333	$254.83	$254.85	$254.80
Purchase #3	$182.91	9.303%	$199.9261	$199.93	$199.95	$199.90
Purchase #4	$195.90	13.552%	$222.4484	$222.45	$222.45	$222.40
Purchase #5	$156.64	7.235%	$167.9729	$167.97	$167.95	$168.00
Purchase #6	$26.77	9.356%	$29.2746	$29.27	$29.25	$29.30
Purchase #7	$88.30	10.814%	$97.8488	$97.85	$97.85	$97.80
7 purchase totals =	$1,010.02		$1,114.8207	$1,114.82	$1,114.80	$1,114.70