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	$94.59	6.240%	$100.4924	$100.49	$100.50	$100.50
Purchase #2	$12.27	4.462%	$12.8175	$12.82	$12.80	$12.80
Purchase #3	$96.84	6.352%	$102.9913	$102.99	$103.00	$103.00
Purchase #4	$37.34	3.424%	$38.6185	$38.62	$38.60	$38.60
Purchase #5	$171.61	8.364%	$185.9635	$185.96	$185.95	$186.00
Purchase #6	$159.76	9.420%	$174.8094	$174.81	$174.80	$174.80
Purchase #7	$66.56	12.516%	$74.8906	$74.89	$74.90	$74.90
7 purchase totals =	$638.97		$690.5832	$690.58	$690.55	$690.60