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	$54.90	13.610%	$62.3719	$62.37	$62.35	$62.40
Purchase #2	$249.68	3.865%	$259.3301	$259.33	$259.35	$259.30
Purchase #3	$49.65	13.378%	$56.2922	$56.29	$56.30	$56.30
Purchase #4	$101.60	8.160%	$109.8906	$109.89	$109.90	$109.90
Purchase #5	$17.51	7.288%	$18.7861	$18.79	$18.80	$18.80
Purchase #6	$41.50	8.850%	$45.1728	$45.17	$45.15	$45.20
Purchase #7	$72.90	9.266%	$79.6549	$79.65	$79.65	$79.70
7 purchase totals =	$587.74		$631.4986	$631.49	$631.50	$631.60