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	$143.30	6.352%	$152.4024	$152.40	$152.40	$152.40
Purchase #2	$131.83	3.529%	$136.4823	$136.48	$136.50	$136.50
Purchase #3	$40.59	13.369%	$46.0165	$46.02	$46.00	$46.00
Purchase #4	$11.93	5.663%	$12.6056	$12.61	$12.60	$12.60
Purchase #5	$170.49	12.753%	$192.2326	$192.23	$192.25	$192.20
Purchase #6	$29.31	12.623%	$33.0098	$33.01	$33.00	$33.00
Purchase #7	$153.27	10.435%	$169.2637	$169.26	$169.25	$169.30
7 purchase totals =	$680.72		$742.0129	$742.01	$742.00	$742.00