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	$142.91	10.156%	$157.4239	$157.42	$157.40	$157.40
Purchase #2	$131.70	11.772%	$147.2037	$147.20	$147.20	$147.20
Purchase #3	$80.41	6.466%	$85.6093	$85.61	$85.60	$85.60
Purchase #4	$228.29	4.484%	$238.5265	$238.53	$238.55	$238.50
Purchase #5	$18.71	9.586%	$20.5035	$20.50	$20.50	$20.50
Purchase #6	$31.57	3.582%	$32.7008	$32.70	$32.70	$32.70
Purchase #7	$238.97	6.674%	$254.9189	$254.92	$254.90	$254.90
7 purchase totals =	$872.56		$936.8866	$936.88	$936.85	$936.80