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	$155.52	10.539%	$171.9103	$171.91	$171.90	$171.90
Purchase #2	$187.42	10.694%	$207.4627	$207.46	$207.45	$207.50
Purchase #3	$193.34	5.424%	$203.8268	$203.83	$203.85	$203.80
Purchase #4	$80.54	10.624%	$89.0966	$89.10	$89.10	$89.10
Purchase #5	$250.36	6.233%	$265.9649	$265.96	$265.95	$266.00
Purchase #6	$33.40	12.512%	$37.579	$37.58	$37.60	$37.60
Purchase #7	$121.66	11.827%	$136.0487	$136.05	$136.05	$136.00
7 purchase totals =	$1,022.24		$1,111.8890	$1,111.89	$1,111.90	$1,111.90