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	$32.41	6.745%	$34.5961	$34.60	$34.60	$34.60
Purchase #2	$79.40	10.553%	$87.7791	$87.78	$87.80	$87.80
Purchase #3	$11.88	5.256%	$12.5044	$12.50	$12.50	$12.50
Purchase #4	$184.88	10.185%	$203.71	$203.71	$203.70	$203.70
Purchase #5	$110.58	11.712%	$123.5311	$123.53	$123.55	$123.50
Purchase #6	$91.82	4.518%	$95.9684	$95.97	$95.95	$96.00
Purchase #7	$39.90	7.559%	$42.916	$42.92	$42.90	$42.90
7 purchase totals =	$550.87		$601.0051	$601.01	$601.00	$601.00