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	$36.74	4.781%	$38.4965	$38.50	$38.50	$38.50
Purchase #2	$38.81	6.255%	$41.2376	$41.24	$41.25	$41.20
Purchase #3	$93.41	3.148%	$96.3505	$96.35	$96.35	$96.40
Purchase #4	$95.99	9.685%	$105.2866	$105.29	$105.30	$105.30
Purchase #5	$176.78	9.713%	$193.9506	$193.95	$193.95	$194.00
Purchase #6	$92.75	13.623%	$105.3853	$105.39	$105.40	$105.40
Purchase #7	$73.60	12.459%	$82.7698	$82.77	$82.75	$82.80
7 purchase totals =	$608.08		$663.4769	$663.49	$663.50	$663.60