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	$131.73	5.637%	$139.1556	$139.16	$139.15	$139.20
Purchase #2	$57.72	11.776%	$64.5171	$64.52	$64.50	$64.50
Purchase #3	$103.98	3.413%	$107.5288	$107.53	$107.55	$107.50
Purchase #4	$86.76	10.460%	$95.8351	$95.84	$95.85	$95.80
Purchase #5	$52.28	12.643%	$58.8898	$58.89	$58.90	$58.90
Purchase #6	$132.51	3.623%	$137.3108	$137.31	$137.30	$137.30
Purchase #7	$38.73	7.437%	$41.6104	$41.61	$41.60	$41.60
7 purchase totals =	$603.71		$644.8476	$644.86	$644.85	$644.80