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	$74.76	8.181%	$80.8761	$80.88	$80.90	$80.90
Purchase #2	$179.84	9.487%	$196.9014	$196.90	$196.90	$196.90
Purchase #3	$81.60	13.154%	$92.3337	$92.33	$92.35	$92.30
Purchase #4	$5.84	13.298%	$6.6166	$6.62	$6.60	$6.60
Purchase #5	$245.93	8.510%	$266.8586	$266.86	$266.85	$266.90
Purchase #6	$157.49	13.167%	$178.2267	$178.23	$178.25	$178.20
Purchase #7	$180.31	10.256%	$198.8026	$198.80	$198.80	$198.80
7 purchase totals =	$925.77		$1,020.6157	$1,020.62	$1,020.65	$1,020.60