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	$170.77	13.329%	$193.5319	$193.53	$193.55	$193.50
Purchase #2	$17.28	7.261%	$18.5347	$18.53	$18.55	$18.50
Purchase #3	$93.85	10.815%	$103.9999	$104.00	$104.00	$104.00
Purchase #4	$28.54	11.761%	$31.8966	$31.90	$31.90	$31.90
Purchase #5	$47.31	13.116%	$53.5152	$53.52	$53.50	$53.50
Purchase #6	$113.65	8.331%	$123.1182	$123.12	$123.10	$123.10
Purchase #7	$14.39	7.859%	$15.5209	$15.52	$15.50	$15.50
7 purchase totals =	$485.79		$540.1174	$540.12	$540.10	$540.00