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	$73.45	13.711%	$83.5207	$83.52	$83.50	$83.50
Purchase #2	$194.30	7.180%	$208.2507	$208.25	$208.25	$208.30
Purchase #3	$99.56	10.306%	$109.8207	$109.82	$109.80	$109.80
Purchase #4	$193.60	4.432%	$202.1804	$202.18	$202.20	$202.20
Purchase #5	$134.41	13.449%	$152.4868	$152.49	$152.50	$152.50
Purchase #6	$125.93	13.692%	$143.1723	$143.17	$143.15	$143.20
Purchase #7	$182.85	11.606%	$204.0716	$204.07	$204.05	$204.10
7 purchase totals =	$1,004.10		$1,103.5032	$1,103.50	$1,103.45	$1,103.60