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	$236.37	8.688%	$256.9058	$256.91	$256.90	$256.90
Purchase #2	$86.27	13.208%	$97.6645	$97.66	$97.65	$97.70
Purchase #3	$5.70	10.663%	$6.3078	$6.31	$6.30	$6.30
Purchase #4	$86.57	11.382%	$96.4234	$96.42	$96.40	$96.40
Purchase #5	$35.55	3.699%	$36.865	$36.87	$36.85	$36.90
Purchase #6	$172.39	10.540%	$190.5599	$190.56	$190.55	$190.60
Purchase #7	$36.93	3.640%	$38.2743	$38.27	$38.25	$38.30
7 purchase totals =	$659.78		$723.0007	$723.00	$722.90	$723.10