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	$123.31	12.873%	$139.1837	$139.18	$139.20	$139.20
Purchase #2	$184.83	7.571%	$198.8235	$198.82	$198.80	$198.80
Purchase #3	$146.90	10.443%	$162.2408	$162.24	$162.25	$162.20
Purchase #4	$167.42	8.754%	$182.0759	$182.08	$182.10	$182.10
Purchase #5	$217.79	12.269%	$244.5107	$244.51	$244.50	$244.50
Purchase #6	$153.71	11.554%	$171.4697	$171.47	$171.45	$171.50
Purchase #7	$148.92	4.435%	$155.5246	$155.52	$155.50	$155.50
7 purchase totals =	$1,142.88		$1,253.8289	$1,253.82	$1,253.80	$1,253.80