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	$32.72	7.543%	$35.1881	$35.19	$35.20	$35.20
Purchase #2	$120.28	4.440%	$125.6204	$125.62	$125.60	$125.60
Purchase #3	$130.70	11.624%	$145.8926	$145.89	$145.90	$145.90
Purchase #4	$215.54	10.615%	$238.4196	$238.42	$238.40	$238.40
Purchase #5	$199.33	8.409%	$216.0917	$216.09	$216.10	$216.10
Purchase #6	$86.55	3.295%	$89.4018	$89.40	$89.40	$89.40
Purchase #7	$63.39	13.548%	$71.9781	$71.98	$72.00	$72.00
7 purchase totals =	$848.51		$922.5923	$922.59	$922.60	$922.60