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	$66.72	5.726%	$70.5404	$70.54	$70.55	$70.50
Purchase #2	$31.93	9.288%	$34.8957	$34.90	$34.90	$34.90
Purchase #3	$139.55	3.542%	$144.4929	$144.49	$144.50	$144.50
Purchase #4	$57.46	12.165%	$64.45	$64.45	$64.45	$64.50
Purchase #5	$148.92	5.550%	$157.1851	$157.19	$157.20	$157.20
Purchase #6	$78.43	12.377%	$88.1373	$88.14	$88.15	$88.10
Purchase #7	$218.84	5.156%	$230.1234	$230.12	$230.10	$230.10
7 purchase totals =	$741.85		$789.8248	$789.83	$789.85	$789.80