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	$245.69	4.311%	$256.2817	$256.28	$256.30	$256.30
Purchase #2	$227.36	6.641%	$242.459	$242.46	$242.45	$242.50
Purchase #3	$26.45	10.565%	$29.2444	$29.24	$29.25	$29.20
Purchase #4	$66.96	6.352%	$71.2133	$71.21	$71.20	$71.20
Purchase #5	$129.59	5.269%	$136.4181	$136.42	$136.40	$136.40
Purchase #6	$165.48	6.410%	$176.0873	$176.09	$176.10	$176.10
Purchase #7	$173.48	8.619%	$188.4322	$188.43	$188.45	$188.40
7 purchase totals =	$1,035.01		$1,100.1360	$1,100.13	$1,100.15	$1,100.10