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	$99.55	4.768%	$104.2965	$104.30	$104.30	$104.30
Purchase #2	$180.69	8.817%	$196.6214	$196.62	$196.60	$196.60
Purchase #3	$74.82	10.796%	$82.8976	$82.90	$82.90	$82.90
Purchase #4	$241.89	4.621%	$253.0677	$253.07	$253.05	$253.10
Purchase #5	$157.95	10.376%	$174.3389	$174.34	$174.35	$174.30
Purchase #6	$45.67	9.551%	$50.0319	$50.03	$50.05	$50.00
Purchase #7	$250.80	10.541%	$277.2368	$277.24	$277.25	$277.20
7 purchase totals =	$1,051.37		$1,138.4908	$1,138.50	$1,138.50	$1,138.40