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	$83.89	6.306%	$89.1801	$89.18	$89.20	$89.20
Purchase #2	$238.96	5.851%	$252.9415	$252.94	$252.95	$252.90
Purchase #3	$90.57	12.426%	$101.8242	$101.82	$101.80	$101.80
Purchase #4	$92.33	9.160%	$100.7874	$100.79	$100.80	$100.80
Purchase #5	$241.99	13.788%	$275.3556	$275.36	$275.35	$275.40
Purchase #6	$166.26	5.465%	$175.3461	$175.35	$175.35	$175.30
Purchase #7	$48.53	5.132%	$51.0206	$51.02	$51.00	$51.00
7 purchase totals =	$962.53		$1,046.4555	$1,046.46	$1,046.45	$1,046.40