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	$123.61	10.352%	$136.4061	$136.41	$136.40	$136.40
Purchase #2	$118.53	7.434%	$127.3415	$127.34	$127.35	$127.30
Purchase #3	$146.62	4.471%	$153.1754	$153.18	$153.20	$153.20
Purchase #4	$199.42	5.219%	$209.8277	$209.83	$209.85	$209.80
Purchase #5	$179.88	13.156%	$203.545	$203.55	$203.55	$203.50
Purchase #6	$229.74	5.488%	$242.3481	$242.35	$242.35	$242.30
Purchase #7	$84.51	8.642%	$91.8134	$91.81	$91.80	$91.80
7 purchase totals =	$1,082.31		$1,164.4572	$1,164.47	$1,164.50	$1,164.30