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	$159.84	4.342%	$166.7803	$166.78	$166.80	$166.80
Purchase #2	$99.96	12.761%	$112.7159	$112.72	$112.70	$112.70
Purchase #3	$75.98	12.488%	$85.4684	$85.47	$85.45	$85.50
Purchase #4	$96.63	3.248%	$99.7685	$99.77	$99.75	$99.80
Purchase #5	$85.66	12.252%	$96.1551	$96.16	$96.15	$96.20
Purchase #6	$147.36	8.160%	$159.3846	$159.38	$159.40	$159.40
Purchase #7	$142.55	11.395%	$158.7936	$158.79	$158.80	$158.80
7 purchase totals =	$807.98		$879.0664	$879.07	$879.05	$879.20