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	$116.82	11.736%	$130.53	$130.53	$130.55	$130.50
Purchase #2	$94.79	10.805%	$105.0321	$105.03	$105.05	$105.00
Purchase #3	$48.62	13.789%	$55.3242	$55.32	$55.30	$55.30
Purchase #4	$170.46	7.250%	$182.8184	$182.82	$182.80	$182.80
Purchase #5	$25.37	10.476%	$28.0278	$28.03	$28.05	$28.00
Purchase #6	$219.78	3.804%	$228.1404	$228.14	$228.15	$228.10
Purchase #7	$40.46	3.365%	$41.8215	$41.82	$41.80	$41.80
7 purchase totals =	$716.30		$771.6944	$771.69	$771.70	$771.50