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	$82.57	8.766%	$89.8081	$89.81	$89.80	$89.80
Purchase #2	$5.74	13.518%	$6.5159	$6.52	$6.50	$6.50
Purchase #3	$230.44	6.491%	$245.3979	$245.40	$245.40	$245.40
Purchase #4	$200.56	7.447%	$215.4957	$215.50	$215.50	$215.50
Purchase #5	$35.38	4.532%	$36.9834	$36.98	$37.00	$37.00
Purchase #6	$247.93	7.746%	$267.1347	$267.13	$267.15	$267.10
Purchase #7	$127.43	7.104%	$136.4826	$136.48	$136.50	$136.50
7 purchase totals =	$930.05		$997.8183	$997.82	$997.85	$997.80