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	$27.29	8.346%	$29.5676	$29.57	$29.55	$29.60
Purchase #2	$5.59	7.222%	$5.9937	$5.99	$6.00	$6.00
Purchase #3	$13.97	11.368%	$15.5581	$15.56	$15.55	$15.60
Purchase #4	$118.47	13.851%	$134.8793	$134.88	$134.90	$134.90
Purchase #5	$87.41	3.690%	$90.6354	$90.64	$90.65	$90.60
Purchase #6	$209.30	4.690%	$219.1162	$219.12	$219.10	$219.10
Purchase #7	$90.83	13.791%	$103.3564	$103.36	$103.35	$103.40
7 purchase totals =	$552.86		$599.1067	$599.12	$599.10	$599.20