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	$29.62	12.327%	$33.2713	$33.27	$33.25	$33.30
Purchase #2	$180.77	6.455%	$192.4387	$192.44	$192.45	$192.40
Purchase #3	$146.39	4.745%	$153.3362	$153.34	$153.35	$153.30
Purchase #4	$47.53	4.648%	$49.7392	$49.74	$49.75	$49.70
Purchase #5	$72.60	5.414%	$76.5306	$76.53	$76.55	$76.50
Purchase #6	$78.81	13.678%	$89.5896	$89.59	$89.60	$89.60
Purchase #7	$55.61	11.557%	$62.0368	$62.04	$62.05	$62.00
7 purchase totals =	$611.33		$656.9424	$656.95	$657.00	$656.80