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	$62.44	13.527%	$70.8863	$70.89	$70.90	$70.90
Purchase #2	$167.49	4.685%	$175.3369	$175.34	$175.35	$175.30
Purchase #3	$246.72	11.133%	$274.1873	$274.19	$274.20	$274.20
Purchase #4	$82.52	12.602%	$92.9192	$92.92	$92.90	$92.90
Purchase #5	$28.67	5.392%	$30.2159	$30.22	$30.20	$30.20
Purchase #6	$159.43	5.306%	$167.8894	$167.89	$167.90	$167.90
Purchase #7	$59.60	3.138%	$61.4702	$61.47	$61.45	$61.50
7 purchase totals =	$806.87		$872.9052	$872.92	$872.90	$872.90