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	$37.28	4.403%	$38.9214	$38.92	$38.90	$38.90
Purchase #2	$133.54	8.484%	$144.8695	$144.87	$144.85	$144.90
Purchase #3	$157.31	4.636%	$164.6029	$164.60	$164.60	$164.60
Purchase #4	$58.82	4.796%	$61.641	$61.64	$61.65	$61.60
Purchase #5	$153.89	5.192%	$161.88	$161.88	$161.90	$161.90
Purchase #6	$87.61	10.654%	$96.944	$96.94	$96.95	$96.90
Purchase #7	$55.43	7.180%	$59.4099	$59.41	$59.40	$59.40
7 purchase totals =	$683.88		$728.2687	$728.26	$728.25	$728.20