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	$33.95	8.389%	$36.7981	$36.80	$36.80	$36.80
Purchase #2	$196.89	3.724%	$204.2222	$204.22	$204.20	$204.20
Purchase #3	$208.98	9.601%	$229.0442	$229.04	$229.05	$229.00
Purchase #4	$160.62	7.276%	$172.3067	$172.31	$172.30	$172.30
Purchase #5	$86.27	9.292%	$94.2862	$94.29	$94.30	$94.30
Purchase #6	$71.28	10.660%	$78.8784	$78.88	$78.90	$78.90
Purchase #7	$65.47	11.108%	$72.7424	$72.74	$72.75	$72.70
7 purchase totals =	$823.46		$888.2782	$888.28	$888.30	$888.20