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	$66.85	6.556%	$71.2327	$71.23	$71.25	$71.20
Purchase #2	$76.25	9.569%	$83.5464	$83.55	$83.55	$83.50
Purchase #3	$130.69	13.379%	$148.175	$148.18	$148.20	$148.20
Purchase #4	$102.54	13.117%	$115.9902	$115.99	$116.00	$116.00
Purchase #5	$82.45	12.231%	$92.5345	$92.53	$92.55	$92.50
Purchase #6	$93.49	12.150%	$104.849	$104.85	$104.85	$104.80
Purchase #7	$179.51	9.516%	$196.5922	$196.59	$196.60	$196.60
7 purchase totals =	$731.78		$812.9200	$812.92	$813.00	$812.80