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	$250.66	10.471%	$276.9066	$276.91	$276.90	$276.90
Purchase #2	$32.35	6.382%	$34.4146	$34.41	$34.40	$34.40
Purchase #3	$94.89	5.523%	$100.1308	$100.13	$100.15	$100.10
Purchase #4	$154.77	8.470%	$167.879	$167.88	$167.90	$167.90
Purchase #5	$101.94	4.221%	$106.2429	$106.24	$106.25	$106.20
Purchase #6	$213.61	7.363%	$229.3381	$229.34	$229.35	$229.30
Purchase #7	$162.64	8.389%	$176.2839	$176.28	$176.30	$176.30
7 purchase totals =	$1,010.86		$1,091.1959	$1,091.19	$1,091.25	$1,091.10