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	$115.92	11.355%	$129.0827	$129.08	$129.10	$129.10
Purchase #2	$103.51	5.312%	$109.0085	$109.01	$109.00	$109.00
Purchase #3	$36.98	11.769%	$41.3322	$41.33	$41.35	$41.30
Purchase #4	$99.59	12.296%	$111.8356	$111.84	$111.85	$111.80
Purchase #5	$37.50	4.800%	$39.3	$39.30	$39.30	$39.30
Purchase #6	$109.76	5.820%	$116.148	$116.15	$116.15	$116.10
Purchase #7	$127.75	3.444%	$132.1497	$132.15	$132.15	$132.10
7 purchase totals =	$631.01		$678.8567	$678.86	$678.90	$678.70