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	$19.72	13.343%	$22.3512	$22.35	$22.35	$22.40
Purchase #2	$67.53	6.648%	$72.0194	$72.02	$72.00	$72.00
Purchase #3	$143.49	13.363%	$162.6646	$162.66	$162.65	$162.70
Purchase #4	$127.35	3.238%	$131.4736	$131.47	$131.45	$131.50
Purchase #5	$152.46	7.683%	$164.1735	$164.17	$164.15	$164.20
Purchase #6	$190.84	7.189%	$204.5595	$204.56	$204.55	$204.60
Purchase #7	$83.39	7.397%	$89.5584	$89.56	$89.55	$89.60
7 purchase totals =	$784.78		$846.8002	$846.79	$846.70	$847.00