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	$138.56	13.235%	$156.8984	$156.90	$156.90	$156.90
Purchase #2	$200.72	3.831%	$208.4096	$208.41	$208.40	$208.40
Purchase #3	$54.88	5.444%	$57.8677	$57.87	$57.85	$57.90
Purchase #4	$34.96	9.865%	$38.4088	$38.41	$38.40	$38.40
Purchase #5	$101.32	4.861%	$106.2452	$106.25	$106.25	$106.20
Purchase #6	$198.38	10.840%	$219.8844	$219.88	$219.90	$219.90
Purchase #7	$150.39	11.438%	$167.5916	$167.59	$167.60	$167.60
7 purchase totals =	$879.21		$955.3057	$955.31	$955.30	$955.30