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	$133.76	13.155%	$151.3561	$151.36	$151.35	$151.40
Purchase #2	$204.60	3.773%	$212.3196	$212.32	$212.30	$212.30
Purchase #3	$130.57	9.175%	$142.5498	$142.55	$142.55	$142.50
Purchase #4	$116.72	5.787%	$123.4746	$123.47	$123.45	$123.50
Purchase #5	$33.46	13.606%	$38.0126	$38.01	$38.00	$38.00
Purchase #6	$185.91	7.103%	$199.1152	$199.12	$199.10	$199.10
Purchase #7	$52.58	4.748%	$55.0765	$55.08	$55.10	$55.10
7 purchase totals =	$857.60		$921.9044	$921.91	$921.85	$921.90