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	$155.80	5.421%	$164.2459	$164.25	$164.25	$164.20
Purchase #2	$242.61	9.568%	$265.8229	$265.82	$265.80	$265.80
Purchase #3	$140.93	6.727%	$150.4104	$150.41	$150.40	$150.40
Purchase #4	$109.87	4.643%	$114.9713	$114.97	$114.95	$115.00
Purchase #5	$34.39	8.237%	$37.2227	$37.22	$37.20	$37.20
Purchase #6	$61.61	6.385%	$65.5438	$65.54	$65.55	$65.50
Purchase #7	$185.92	3.174%	$191.8211	$191.82	$191.80	$191.80
7 purchase totals =	$931.13		$990.0381	$990.03	$989.95	$989.90