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	$164.91	12.730%	$185.903	$185.90	$185.90	$185.90
Purchase #2	$154.30	9.205%	$168.5033	$168.50	$168.50	$168.50
Purchase #3	$130.41	6.213%	$138.5124	$138.51	$138.50	$138.50
Purchase #4	$40.61	5.725%	$42.9349	$42.93	$42.95	$42.90
Purchase #5	$63.75	8.292%	$69.0362	$69.04	$69.05	$69.00
Purchase #6	$148.34	3.707%	$153.839	$153.84	$153.85	$153.80
Purchase #7	$123.54	5.309%	$130.0987	$130.10	$130.10	$130.10
7 purchase totals =	$825.86		$888.8275	$888.82	$888.85	$888.70