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	$120.98	8.296%	$131.0165	$131.02	$131.00	$131.00
Purchase #2	$226.76	5.331%	$238.8486	$238.85	$238.85	$238.80
Purchase #3	$115.87	6.474%	$123.3714	$123.37	$123.35	$123.40
Purchase #4	$174.94	13.105%	$197.8659	$197.87	$197.85	$197.90
Purchase #5	$86.55	11.218%	$96.2592	$96.26	$96.25	$96.30
Purchase #6	$142.84	3.449%	$147.7666	$147.77	$147.75	$147.80
Purchase #7	$70.87	10.290%	$78.1625	$78.16	$78.15	$78.20
7 purchase totals =	$938.81		$1,013.2907	$1,013.30	$1,013.20	$1,013.40