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	$169.94	4.228%	$177.1251	$177.13	$177.15	$177.10
Purchase #2	$105.70	3.305%	$109.1934	$109.19	$109.20	$109.20
Purchase #3	$37.37	4.310%	$38.9806	$38.98	$39.00	$39.00
Purchase #4	$69.76	3.551%	$72.2372	$72.24	$72.25	$72.20
Purchase #5	$215.54	13.485%	$244.6056	$244.61	$244.60	$244.60
Purchase #6	$215.87	13.235%	$244.4404	$244.44	$244.45	$244.40
Purchase #7	$39.28	9.183%	$42.8871	$42.89	$42.90	$42.90
7 purchase totals =	$853.46		$929.4694	$929.48	$929.55	$929.40