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	$82.64	11.736%	$92.3386	$92.34	$92.35	$92.30
Purchase #2	$130.79	8.153%	$141.4533	$141.45	$141.45	$141.50
Purchase #3	$160.93	3.423%	$166.4386	$166.44	$166.45	$166.40
Purchase #4	$169.76	12.151%	$190.3875	$190.39	$190.40	$190.40
Purchase #5	$6.79	6.300%	$7.2178	$7.22	$7.20	$7.20
Purchase #6	$98.40	13.573%	$111.7558	$111.76	$111.75	$111.80
Purchase #7	$18.75	12.577%	$21.1082	$21.11	$21.10	$21.10
7 purchase totals =	$668.06		$730.6998	$730.71	$730.70	$730.70