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	$83.56	7.786%	$90.066	$90.07	$90.05	$90.10
Purchase #2	$78.94	12.868%	$89.098	$89.10	$89.10	$89.10
Purchase #3	$116.96	5.415%	$123.2934	$123.29	$123.30	$123.30
Purchase #4	$59.62	5.366%	$62.8192	$62.82	$62.80	$62.80
Purchase #5	$144.77	7.587%	$155.7537	$155.75	$155.75	$155.80
Purchase #6	$109.47	12.459%	$123.1089	$123.11	$123.10	$123.10
Purchase #7	$216.92	12.564%	$244.1738	$244.17	$244.15	$244.20
7 purchase totals =	$810.24		$888.3130	$888.31	$888.25	$888.40