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	$135.87	6.298%	$144.4271	$144.43	$144.45	$144.40
Purchase #2	$130.61	11.122%	$145.1364	$145.14	$145.15	$145.10
Purchase #3	$125.49	9.663%	$137.6161	$137.62	$137.60	$137.60
Purchase #4	$137.98	10.200%	$152.054	$152.05	$152.05	$152.10
Purchase #5	$171.78	11.570%	$191.6549	$191.65	$191.65	$191.70
Purchase #6	$63.56	11.436%	$70.8287	$70.83	$70.85	$70.80
Purchase #7	$107.59	6.473%	$114.5543	$114.55	$114.55	$114.60
7 purchase totals =	$872.88		$956.2715	$956.27	$956.30	$956.30