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	$41.67	9.218%	$45.5111	$45.51	$45.50	$45.50
Purchase #2	$39.62	13.858%	$45.1105	$45.11	$45.10	$45.10
Purchase #3	$219.39	4.506%	$229.2757	$229.28	$229.30	$229.30
Purchase #4	$231.35	6.701%	$246.8528	$246.85	$246.85	$246.90
Purchase #5	$110.88	8.107%	$119.869	$119.87	$119.85	$119.90
Purchase #6	$249.28	13.616%	$283.222	$283.22	$283.20	$283.20
Purchase #7	$102.63	8.329%	$111.1781	$111.18	$111.20	$111.20
7 purchase totals =	$994.82		$1,081.0192	$1,081.02	$1,081.00	$1,081.10