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	$82.57	9.396%	$90.3283	$90.33	$90.35	$90.30
Purchase #2	$171.42	7.505%	$184.2851	$184.29	$184.30	$184.30
Purchase #3	$248.94	3.822%	$258.4545	$258.45	$258.45	$258.50
Purchase #4	$234.58	6.556%	$249.9591	$249.96	$249.95	$250.00
Purchase #5	$126.95	11.257%	$141.2408	$141.24	$141.25	$141.20
Purchase #6	$37.49	7.777%	$40.4056	$40.41	$40.40	$40.40
Purchase #7	$236.43	6.134%	$250.9326	$250.93	$250.95	$250.90
7 purchase totals =	$1,138.38		$1,215.6060	$1,215.61	$1,215.65	$1,215.60