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	$122.33	4.251%	$127.5302	$127.53	$127.55	$127.50
Purchase #2	$124.34	5.554%	$131.2458	$131.25	$131.25	$131.20
Purchase #3	$27.66	10.332%	$30.5178	$30.52	$30.50	$30.50
Purchase #4	$83.42	6.150%	$88.5503	$88.55	$88.55	$88.60
Purchase #5	$12.37	4.671%	$12.9478	$12.95	$12.95	$12.90
Purchase #6	$82.27	7.306%	$88.2806	$88.28	$88.30	$88.30
Purchase #7	$148.99	5.300%	$156.8865	$156.89	$156.90	$156.90
7 purchase totals =	$601.38		$635.9590	$635.97	$636.00	$635.90