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	$126.53	12.289%	$142.0793	$142.08	$142.10	$142.10
Purchase #2	$96.30	9.718%	$105.6584	$105.66	$105.65	$105.70
Purchase #3	$245.34	8.511%	$266.2209	$266.22	$266.20	$266.20
Purchase #4	$74.56	3.720%	$77.3336	$77.33	$77.35	$77.30
Purchase #5	$105.68	9.746%	$115.9796	$115.98	$116.00	$116.00
Purchase #6	$81.60	9.514%	$89.3634	$89.36	$89.35	$89.40
Purchase #7	$93.77	10.735%	$103.8362	$103.84	$103.85	$103.80
7 purchase totals =	$823.78		$900.4714	$900.47	$900.50	$900.50