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	$29.99	11.726%	$33.5066	$33.51	$33.50	$33.50
Purchase #2	$164.81	4.798%	$172.7176	$172.72	$172.70	$172.70
Purchase #3	$123.84	13.516%	$140.5782	$140.58	$140.60	$140.60
Purchase #4	$248.27	6.160%	$263.5634	$263.56	$263.55	$263.60
Purchase #5	$97.48	7.568%	$104.8573	$104.86	$104.85	$104.90
Purchase #6	$249.36	9.655%	$273.4357	$273.44	$273.45	$273.40
Purchase #7	$158.98	9.309%	$173.7794	$173.78	$173.80	$173.80
7 purchase totals =	$1,072.73		$1,162.4382	$1,162.45	$1,162.45	$1,162.50