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	$97.78	5.685%	$103.3388	$103.34	$103.35	$103.30
Purchase #2	$123.38	7.230%	$132.3004	$132.30	$132.30	$132.30
Purchase #3	$221.40	13.298%	$250.8418	$250.84	$250.85	$250.80
Purchase #4	$86.75	13.282%	$98.2721	$98.27	$98.25	$98.30
Purchase #5	$245.43	8.743%	$266.8879	$266.89	$266.90	$266.90
Purchase #6	$33.62	9.114%	$36.6841	$36.68	$36.70	$36.70
Purchase #7	$92.28	9.359%	$100.9165	$100.92	$100.90	$100.90
7 purchase totals =	$900.64		$989.2416	$989.24	$989.25	$989.20