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	$86.35	4.341%	$90.0985	$90.10	$90.10	$90.10
Purchase #2	$245.73	10.722%	$272.0772	$272.08	$272.10	$272.10
Purchase #3	$181.80	8.639%	$197.5057	$197.51	$197.50	$197.50
Purchase #4	$137.57	10.444%	$151.9378	$151.94	$151.95	$151.90
Purchase #5	$19.52	6.856%	$20.8583	$20.86	$20.85	$20.90
Purchase #6	$33.36	5.224%	$35.1027	$35.10	$35.10	$35.10
Purchase #7	$84.87	5.329%	$89.3927	$89.39	$89.40	$89.40
7 purchase totals =	$789.20		$856.9729	$856.98	$857.00	$857.00