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	$94.88	13.873%	$108.0427	$108.04	$108.05	$108.00
Purchase #2	$135.46	8.760%	$147.3263	$147.33	$147.35	$147.30
Purchase #3	$28.90	3.621%	$29.9465	$29.95	$29.95	$29.90
Purchase #4	$182.64	4.760%	$191.3337	$191.33	$191.35	$191.30
Purchase #5	$43.29	5.857%	$45.8255	$45.83	$45.85	$45.80
Purchase #6	$198.30	11.725%	$221.5507	$221.55	$221.55	$221.60
Purchase #7	$77.82	11.170%	$86.5125	$86.51	$86.50	$86.50
7 purchase totals =	$761.29		$830.5379	$830.54	$830.60	$830.40