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	$79.67	5.229%	$83.8359	$83.84	$83.85	$83.80
Purchase #2	$99.98	12.831%	$112.8084	$112.81	$112.80	$112.80
Purchase #3	$194.78	8.608%	$211.5467	$211.55	$211.55	$211.50
Purchase #4	$166.60	7.130%	$178.4786	$178.48	$178.50	$178.50
Purchase #5	$225.54	3.717%	$233.9233	$233.92	$233.90	$233.90
Purchase #6	$218.73	3.281%	$225.9065	$225.91	$225.90	$225.90
Purchase #7	$164.45	6.369%	$174.9238	$174.92	$174.90	$174.90
7 purchase totals =	$1,149.75		$1,221.4232	$1,221.43	$1,221.40	$1,221.30