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	$223.52	7.355%	$239.9599	$239.96	$239.95	$240.00
Purchase #2	$36.86	7.741%	$39.7133	$39.71	$39.70	$39.70
Purchase #3	$84.91	13.871%	$96.6879	$96.69	$96.70	$96.70
Purchase #4	$38.32	8.525%	$41.5868	$41.59	$41.60	$41.60
Purchase #5	$37.92	11.153%	$42.1492	$42.15	$42.15	$42.10
Purchase #6	$135.70	12.435%	$152.5743	$152.57	$152.55	$152.60
Purchase #7	$113.52	13.509%	$128.8554	$128.86	$128.85	$128.90
7 purchase totals =	$670.75		$741.5268	$741.53	$741.50	$741.60