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	$244.98	11.536%	$273.2409	$273.24	$273.25	$273.20
Purchase #2	$43.69	13.658%	$49.6572	$49.66	$49.65	$49.70
Purchase #3	$248.63	6.231%	$264.1221	$264.12	$264.10	$264.10
Purchase #4	$72.83	10.319%	$80.3453	$80.35	$80.35	$80.30
Purchase #5	$229.64	8.805%	$249.8598	$249.86	$249.85	$249.90
Purchase #6	$172.50	10.339%	$190.3348	$190.33	$190.35	$190.30
Purchase #7	$81.47	11.539%	$90.8708	$90.87	$90.85	$90.90
7 purchase totals =	$1,093.74		$1,198.4309	$1,198.43	$1,198.40	$1,198.40