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	$232.75	6.222%	$247.2317	$247.23	$247.25	$247.20
Purchase #2	$165.94	5.364%	$174.841	$174.84	$174.85	$174.80
Purchase #3	$74.69	10.234%	$82.3338	$82.33	$82.35	$82.30
Purchase #4	$69.98	3.500%	$72.4293	$72.43	$72.45	$72.40
Purchase #5	$169.43	8.786%	$184.3161	$184.32	$184.30	$184.30
Purchase #6	$158.83	13.406%	$180.1227	$180.12	$180.10	$180.10
Purchase #7	$26.34	4.813%	$27.6077	$27.61	$27.60	$27.60
7 purchase totals =	$897.96		$968.8823	$968.88	$968.90	$968.70