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	$24.50	11.589%	$27.3393	$27.34	$27.35	$27.30
Purchase #2	$182.30	3.495%	$188.6714	$188.67	$188.65	$188.70
Purchase #3	$32.78	13.140%	$37.0873	$37.09	$37.10	$37.10
Purchase #4	$174.66	12.316%	$196.1711	$196.17	$196.15	$196.20
Purchase #5	$197.84	4.562%	$206.8655	$206.87	$206.85	$206.90
Purchase #6	$101.96	6.165%	$108.2458	$108.25	$108.25	$108.20
Purchase #7	$121.39	8.442%	$131.6377	$131.64	$131.65	$131.60
7 purchase totals =	$835.43		$896.0181	$896.03	$896.00	$896.00