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	$26.26	5.617%	$27.735	$27.74	$27.75	$27.70
Purchase #2	$48.46	10.246%	$53.4252	$53.43	$53.45	$53.40
Purchase #3	$79.46	4.683%	$83.1811	$83.18	$83.20	$83.20
Purchase #4	$236.72	13.369%	$268.3671	$268.37	$268.35	$268.40
Purchase #5	$86.50	4.327%	$90.2429	$90.24	$90.25	$90.20
Purchase #6	$228.99	4.229%	$238.674	$238.67	$238.65	$238.70
Purchase #7	$29.30	5.849%	$31.0138	$31.01	$31.00	$31.00
7 purchase totals =	$735.69		$792.6391	$792.64	$792.65	$792.60