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	$30.56	6.292%	$32.4828	$32.48	$32.50	$32.50
Purchase #2	$105.83	10.432%	$116.8702	$116.87	$116.85	$116.90
Purchase #3	$173.99	8.645%	$189.0314	$189.03	$189.05	$189.00
Purchase #4	$142.53	6.181%	$151.3398	$151.34	$151.35	$151.30
Purchase #5	$17.86	5.699%	$18.8778	$18.88	$18.90	$18.90
Purchase #6	$233.70	3.786%	$242.5479	$242.55	$242.55	$242.50
Purchase #7	$244.25	6.718%	$260.6587	$260.66	$260.65	$260.70
7 purchase totals =	$948.72		$1,011.8086	$1,011.81	$1,011.85	$1,011.80