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	$145.78	8.600%	$158.3171	$158.32	$158.30	$158.30
Purchase #2	$179.47	3.530%	$185.8053	$185.81	$185.80	$185.80
Purchase #3	$159.57	9.792%	$175.1951	$175.20	$175.20	$175.20
Purchase #4	$73.85	11.839%	$82.5931	$82.59	$82.60	$82.60
Purchase #5	$89.49	7.365%	$96.0809	$96.08	$96.10	$96.10
Purchase #6	$143.69	6.660%	$153.2598	$153.26	$153.25	$153.30
Purchase #7	$170.32	10.828%	$188.7622	$188.76	$188.75	$188.80
7 purchase totals =	$962.17		$1,040.0135	$1,040.02	$1,040.00	$1,040.10