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	$170.92	10.316%	$188.5521	$188.55	$188.55	$188.60
Purchase #2	$135.78	6.435%	$144.5174	$144.52	$144.50	$144.50
Purchase #3	$235.90	11.623%	$263.3187	$263.32	$263.30	$263.30
Purchase #4	$37.63	11.861%	$42.0933	$42.09	$42.10	$42.10
Purchase #5	$87.37	11.104%	$97.0716	$97.07	$97.05	$97.10
Purchase #6	$81.39	11.780%	$90.9777	$90.98	$91.00	$91.00
Purchase #7	$55.31	10.830%	$61.3001	$61.30	$61.30	$61.30
7 purchase totals =	$804.30		$887.8309	$887.83	$887.80	$887.90