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	$204.33	3.692%	$211.8739	$211.87	$211.85	$211.90
Purchase #2	$118.90	10.115%	$130.9267	$130.93	$130.95	$130.90
Purchase #3	$146.78	4.175%	$152.9081	$152.91	$152.90	$152.90
Purchase #4	$34.28	13.334%	$38.8509	$38.85	$38.85	$38.90
Purchase #5	$152.49	5.791%	$161.3207	$161.32	$161.30	$161.30
Purchase #6	$40.89	3.796%	$42.4422	$42.44	$42.45	$42.40
Purchase #7	$229.29	5.274%	$241.3828	$241.38	$241.40	$241.40
7 purchase totals =	$926.96		$979.7053	$979.70	$979.70	$979.70