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	$135.32	10.192%	$149.1118	$149.11	$149.10	$149.10
Purchase #2	$54.86	4.650%	$57.411	$57.41	$57.40	$57.40
Purchase #3	$41.45	10.450%	$45.7815	$45.78	$45.80	$45.80
Purchase #4	$89.60	13.228%	$101.4523	$101.45	$101.45	$101.50
Purchase #5	$44.37	13.591%	$50.4003	$50.40	$50.40	$50.40
Purchase #6	$83.85	9.764%	$92.0371	$92.04	$92.05	$92.00
Purchase #7	$155.31	13.700%	$176.5875	$176.59	$176.60	$176.60
7 purchase totals =	$604.76		$672.7815	$672.78	$672.80	$672.80