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	$41.34	10.393%	$45.6365	$45.64	$45.65	$45.60
Purchase #2	$29.69	8.270%	$32.1454	$32.15	$32.15	$32.10
Purchase #3	$242.65	5.457%	$255.8914	$255.89	$255.90	$255.90
Purchase #4	$67.66	13.566%	$76.8388	$76.84	$76.85	$76.80
Purchase #5	$172.52	4.417%	$180.1402	$180.14	$180.15	$180.10
Purchase #6	$90.78	7.746%	$97.8118	$97.81	$97.80	$97.80
Purchase #7	$213.30	13.388%	$241.8566	$241.86	$241.85	$241.90
7 purchase totals =	$857.94		$930.3207	$930.33	$930.35	$930.20