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	$116.43	5.747%	$123.1212	$123.12	$123.10	$123.10
Purchase #2	$243.80	3.588%	$252.5475	$252.55	$252.55	$252.50
Purchase #3	$172.82	12.565%	$194.5348	$194.53	$194.55	$194.50
Purchase #4	$163.59	9.618%	$179.3241	$179.32	$179.30	$179.30
Purchase #5	$134.72	7.741%	$145.1487	$145.15	$145.15	$145.10
Purchase #6	$139.78	5.777%	$147.8551	$147.86	$147.85	$147.90
Purchase #7	$8.32	6.732%	$8.8801	$8.88	$8.90	$8.90
7 purchase totals =	$979.46		$1,051.4115	$1,051.41	$1,051.40	$1,051.30