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	$223.37	12.215%	$250.6546	$250.65	$250.65	$250.70
Purchase #2	$66.33	13.341%	$75.1791	$75.18	$75.20	$75.20
Purchase #3	$108.52	3.704%	$112.5396	$112.54	$112.55	$112.50
Purchase #4	$82.32	8.868%	$89.6201	$89.62	$89.60	$89.60
Purchase #5	$141.75	12.810%	$159.9082	$159.91	$159.90	$159.90
Purchase #6	$145.98	4.256%	$152.1929	$152.19	$152.20	$152.20
Purchase #7	$69.53	4.236%	$72.4753	$72.48	$72.50	$72.50
7 purchase totals =	$837.80		$912.5698	$912.57	$912.60	$912.60