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	$81.89	6.734%	$87.4045	$87.40	$87.40	$87.40
Purchase #2	$44.84	9.800%	$49.2343	$49.23	$49.25	$49.20
Purchase #3	$215.87	10.613%	$238.7803	$238.78	$238.80	$238.80
Purchase #4	$30.42	4.380%	$31.7524	$31.75	$31.75	$31.80
Purchase #5	$235.28	13.557%	$267.1769	$267.18	$267.20	$267.20
Purchase #6	$39.53	6.664%	$42.1643	$42.16	$42.15	$42.20
Purchase #7	$57.68	3.178%	$59.5131	$59.51	$59.50	$59.50
7 purchase totals =	$705.51		$776.0258	$776.01	$776.05	$776.10