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	$139.92	3.536%	$144.8676	$144.87	$144.85	$144.90
Purchase #2	$237.69	3.567%	$246.1684	$246.17	$246.15	$246.20
Purchase #3	$68.63	13.108%	$77.626	$77.63	$77.65	$77.60
Purchase #4	$79.54	12.299%	$89.3226	$89.32	$89.30	$89.30
Purchase #5	$36.70	6.766%	$39.1831	$39.18	$39.20	$39.20
Purchase #6	$168.31	13.827%	$191.5822	$191.58	$191.60	$191.60
Purchase #7	$141.59	6.355%	$150.588	$150.59	$150.60	$150.60
7 purchase totals =	$872.38		$939.3379	$939.34	$939.35	$939.40