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	$110.63	13.264%	$125.304	$125.30	$125.30	$125.30
Purchase #2	$117.31	6.155%	$124.5304	$124.53	$124.55	$124.50
Purchase #3	$29.73	6.630%	$31.7011	$31.70	$31.70	$31.70
Purchase #4	$40.52	13.198%	$45.8678	$45.87	$45.85	$45.90
Purchase #5	$127.80	10.675%	$141.4427	$141.44	$141.45	$141.40
Purchase #6	$176.54	4.809%	$185.0298	$185.03	$185.05	$185.00
Purchase #7	$109.83	13.434%	$124.5846	$124.58	$124.60	$124.60
7 purchase totals =	$712.36		$778.4604	$778.45	$778.50	$778.40