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	$223.49	12.644%	$251.7481	$251.75	$251.75	$251.70
Purchase #2	$113.50	13.103%	$128.3719	$128.37	$128.35	$128.40
Purchase #3	$145.70	12.808%	$164.3613	$164.36	$164.35	$164.40
Purchase #4	$77.39	10.726%	$85.6909	$85.69	$85.70	$85.70
Purchase #5	$72.79	7.359%	$78.1466	$78.15	$78.15	$78.10
Purchase #6	$97.66	3.623%	$101.1982	$101.20	$101.20	$101.20
Purchase #7	$180.28	10.311%	$198.8687	$198.87	$198.85	$198.90
7 purchase totals =	$910.81		$1,008.3857	$1,008.39	$1,008.35	$1,008.40