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	$16.56	13.365%	$18.7732	$18.77	$18.75	$18.80
Purchase #2	$202.91	6.606%	$216.3142	$216.31	$216.30	$216.30
Purchase #3	$212.79	12.191%	$238.7312	$238.73	$238.75	$238.70
Purchase #4	$89.47	12.777%	$100.9016	$100.90	$100.90	$100.90
Purchase #5	$122.31	13.550%	$138.883	$138.88	$138.90	$138.90
Purchase #6	$56.47	8.213%	$61.1079	$61.11	$61.10	$61.10
Purchase #7	$99.73	5.444%	$105.1593	$105.16	$105.15	$105.20
7 purchase totals =	$800.24		$879.8704	$879.86	$879.85	$879.90