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	$131.54	6.819%	$140.5097	$140.51	$140.50	$140.50
Purchase #2	$208.25	10.660%	$230.4495	$230.45	$230.45	$230.40
Purchase #3	$144.84	13.851%	$164.9018	$164.90	$164.90	$164.90
Purchase #4	$172.50	10.649%	$190.8695	$190.87	$190.85	$190.90
Purchase #5	$184.42	5.364%	$194.3123	$194.31	$194.30	$194.30
Purchase #6	$106.36	10.107%	$117.1098	$117.11	$117.10	$117.10
Purchase #7	$238.26	10.158%	$262.4625	$262.46	$262.45	$262.50
7 purchase totals =	$1,186.17		$1,300.6151	$1,300.61	$1,300.55	$1,300.60