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	$26.60	8.294%	$28.8062	$28.81	$28.80	$28.80
Purchase #2	$53.89	8.254%	$58.3381	$58.34	$58.35	$58.30
Purchase #3	$59.57	12.230%	$66.8554	$66.86	$66.85	$66.90
Purchase #4	$54.90	6.430%	$58.4301	$58.43	$58.45	$58.40
Purchase #5	$52.96	7.201%	$56.7736	$56.77	$56.75	$56.80
Purchase #6	$98.79	12.676%	$111.3126	$111.31	$111.30	$111.30
Purchase #7	$101.98	12.319%	$114.5429	$114.54	$114.55	$114.50
7 purchase totals =	$448.69		$495.0589	$495.06	$495.05	$495.00