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	$243.37	11.151%	$270.5082	$270.51	$270.50	$270.50
Purchase #2	$86.43	4.866%	$90.6357	$90.64	$90.65	$90.60
Purchase #3	$239.71	8.246%	$259.4765	$259.48	$259.50	$259.50
Purchase #4	$109.26	13.764%	$124.2985	$124.30	$124.30	$124.30
Purchase #5	$246.47	4.195%	$256.8094	$256.81	$256.80	$256.80
Purchase #6	$90.86	7.726%	$97.8798	$97.88	$97.90	$97.90
Purchase #7	$69.90	4.603%	$73.1175	$73.12	$73.10	$73.10
7 purchase totals =	$1,086.00		$1,172.7256	$1,172.74	$1,172.75	$1,172.70