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	$150.49	4.151%	$156.7368	$156.74	$156.75	$156.70
Purchase #2	$144.75	5.201%	$152.2784	$152.28	$152.30	$152.30
Purchase #3	$235.81	12.346%	$264.9231	$264.92	$264.90	$264.90
Purchase #4	$12.53	11.794%	$14.0078	$14.01	$14.00	$14.00
Purchase #5	$76.98	10.769%	$85.27	$85.27	$85.25	$85.30
Purchase #6	$109.53	7.600%	$117.8543	$117.85	$117.85	$117.90
Purchase #7	$90.48	4.314%	$94.3833	$94.38	$94.40	$94.40
7 purchase totals =	$820.57		$885.4537	$885.45	$885.45	$885.50