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	$75.43	7.336%	$80.9635	$80.96	$80.95	$81.00
Purchase #2	$57.97	13.145%	$65.5902	$65.59	$65.60	$65.60
Purchase #3	$73.72	8.717%	$80.1462	$80.15	$80.15	$80.10
Purchase #4	$154.60	12.271%	$173.571	$173.57	$173.55	$173.60
Purchase #5	$85.96	10.232%	$94.7554	$94.76	$94.75	$94.80
Purchase #6	$133.37	6.692%	$142.2951	$142.30	$142.30	$142.30
Purchase #7	$30.56	5.714%	$32.3062	$32.31	$32.30	$32.30
7 purchase totals =	$611.61		$669.6276	$669.64	$669.60	$669.70