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	$79.84	12.610%	$89.9078	$89.91	$89.90	$89.90
Purchase #2	$93.49	10.792%	$103.5794	$103.58	$103.60	$103.60
Purchase #3	$35.98	6.258%	$38.2316	$38.23	$38.25	$38.20
Purchase #4	$125.85	4.604%	$131.6441	$131.64	$131.65	$131.60
Purchase #5	$21.38	4.782%	$22.4024	$22.40	$22.40	$22.40
Purchase #6	$35.88	8.496%	$38.9284	$38.93	$38.95	$38.90
Purchase #7	$31.61	7.246%	$33.9005	$33.90	$33.90	$33.90
7 purchase totals =	$424.03		$458.5942	$458.59	$458.65	$458.50