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	$143.65	6.554%	$153.0648	$153.06	$153.05	$153.10
Purchase #2	$45.74	10.165%	$50.3895	$50.39	$50.40	$50.40
Purchase #3	$111.85	11.762%	$125.0058	$125.01	$125.00	$125.00
Purchase #4	$125.27	9.742%	$137.4738	$137.47	$137.45	$137.50
Purchase #5	$72.89	5.124%	$76.6249	$76.62	$76.60	$76.60
Purchase #6	$84.39	3.124%	$87.0263	$87.03	$87.05	$87.00
Purchase #7	$79.69	3.635%	$82.5867	$82.59	$82.60	$82.60
7 purchase totals =	$663.48		$712.1718	$712.17	$712.15	$712.20