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	$52.49	12.691%	$59.1515	$59.15	$59.15	$59.20
Purchase #2	$140.32	4.666%	$146.8673	$146.87	$146.85	$146.90
Purchase #3	$210.56	12.200%	$236.2483	$236.25	$236.25	$236.20
Purchase #4	$166.79	5.116%	$175.323	$175.32	$175.30	$175.30
Purchase #5	$137.58	12.136%	$154.2767	$154.28	$154.30	$154.30
Purchase #6	$120.43	5.579%	$127.1488	$127.15	$127.15	$127.10
Purchase #7	$130.36	11.377%	$145.1911	$145.19	$145.20	$145.20
7 purchase totals =	$958.53		$1,044.2067	$1,044.21	$1,044.20	$1,044.20