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	$225.79	12.871%	$254.8514	$254.85	$254.85	$254.90
Purchase #2	$69.36	4.757%	$72.6595	$72.66	$72.65	$72.70
Purchase #3	$153.61	6.714%	$163.9234	$163.92	$163.90	$163.90
Purchase #4	$130.95	10.340%	$144.4902	$144.49	$144.50	$144.50
Purchase #5	$216.72	11.377%	$241.3762	$241.38	$241.40	$241.40
Purchase #6	$170.96	8.382%	$185.2899	$185.29	$185.30	$185.30
Purchase #7	$217.71	10.478%	$240.5217	$240.52	$240.50	$240.50
7 purchase totals =	$1,185.10		$1,303.1123	$1,303.11	$1,303.10	$1,303.20