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	$37.83	13.191%	$42.8202	$42.82	$42.80	$42.80
Purchase #2	$100.78	8.204%	$109.048	$109.05	$109.05	$109.00
Purchase #3	$143.70	3.483%	$148.7051	$148.71	$148.70	$148.70
Purchase #4	$89.29	8.252%	$96.6582	$96.66	$96.65	$96.70
Purchase #5	$236.51	9.341%	$258.6024	$258.60	$258.60	$258.60
Purchase #6	$155.62	6.686%	$166.0248	$166.02	$166.00	$166.00
Purchase #7	$80.46	7.259%	$86.3006	$86.30	$86.30	$86.30
7 purchase totals =	$844.19		$908.1593	$908.16	$908.10	$908.10