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	$125.67	13.441%	$142.5613	$142.56	$142.55	$142.60
Purchase #2	$130.44	11.541%	$145.4941	$145.49	$145.50	$145.50
Purchase #3	$234.98	3.778%	$243.8575	$243.86	$243.85	$243.90
Purchase #4	$249.73	10.418%	$275.7469	$275.75	$275.75	$275.70
Purchase #5	$99.94	11.529%	$111.4621	$111.46	$111.45	$111.50
Purchase #6	$48.53	8.824%	$52.8123	$52.81	$52.80	$52.80
Purchase #7	$101.93	6.837%	$108.899	$108.90	$108.90	$108.90
7 purchase totals =	$991.22		$1,080.8332	$1,080.83	$1,080.80	$1,080.90