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	$25.52	7.261%	$27.373	$27.37	$27.35	$27.40
Purchase #2	$32.86	9.864%	$36.1013	$36.10	$36.10	$36.10
Purchase #3	$155.38	8.436%	$168.4879	$168.49	$168.50	$168.50
Purchase #4	$144.67	7.451%	$155.4494	$155.45	$155.45	$155.40
Purchase #5	$222.77	12.230%	$250.0148	$250.01	$250.00	$250.00
Purchase #6	$20.94	3.640%	$21.7022	$21.70	$21.70	$21.70
Purchase #7	$149.84	10.409%	$165.4368	$165.44	$165.45	$165.40
7 purchase totals =	$751.98		$824.5654	$824.56	$824.55	$824.50