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	$6.76	11.293%	$7.5234	$7.52	$7.50	$7.50
Purchase #2	$157.96	3.119%	$162.8868	$162.89	$162.90	$162.90
Purchase #3	$248.56	7.230%	$266.5309	$266.53	$266.55	$266.50
Purchase #4	$219.46	6.566%	$233.8697	$233.87	$233.85	$233.90
Purchase #5	$163.29	11.145%	$181.4887	$181.49	$181.50	$181.50
Purchase #6	$112.34	6.778%	$119.9544	$119.95	$119.95	$120.00
Purchase #7	$154.79	12.107%	$173.5304	$173.53	$173.55	$173.50
7 purchase totals =	$1,063.16		$1,145.7843	$1,145.78	$1,145.80	$1,145.80