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	$153.36	11.675%	$171.2648	$171.26	$171.25	$171.30
Purchase #2	$55.86	13.607%	$63.4609	$63.46	$63.45	$63.50
Purchase #3	$237.95	9.385%	$260.2816	$260.28	$260.30	$260.30
Purchase #4	$16.58	11.367%	$18.4646	$18.46	$18.45	$18.50
Purchase #5	$53.59	4.331%	$55.911	$55.91	$55.90	$55.90
Purchase #6	$39.32	7.247%	$42.1695	$42.17	$42.15	$42.20
Purchase #7	$210.80	8.583%	$228.893	$228.89	$228.90	$228.90
7 purchase totals =	$767.46		$840.4454	$840.43	$840.40	$840.60