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	$28.96	4.334%	$30.2151	$30.22	$30.20	$30.20
Purchase #2	$78.81	5.203%	$82.9105	$82.91	$82.90	$82.90
Purchase #3	$158.64	6.704%	$169.2752	$169.28	$169.30	$169.30
Purchase #4	$67.89	4.704%	$71.0835	$71.08	$71.10	$71.10
Purchase #5	$217.81	4.861%	$228.3977	$228.40	$228.40	$228.40
Purchase #6	$21.90	3.155%	$22.5909	$22.59	$22.60	$22.60
Purchase #7	$27.27	8.303%	$29.5342	$29.53	$29.55	$29.50
7 purchase totals =	$601.28		$634.0071	$634.01	$634.05	$634.00