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	$50.31	3.189%	$51.9144	$51.91	$51.90	$51.90
Purchase #2	$239.50	12.839%	$270.2494	$270.25	$270.25	$270.20
Purchase #3	$127.32	7.351%	$136.6793	$136.68	$136.70	$136.70
Purchase #4	$178.87	6.577%	$190.6343	$190.63	$190.65	$190.60
Purchase #5	$96.84	12.779%	$109.2152	$109.22	$109.20	$109.20
Purchase #6	$237.57	13.791%	$270.3333	$270.33	$270.35	$270.30
Purchase #7	$146.94	13.716%	$167.0943	$167.09	$167.10	$167.10
7 purchase totals =	$1,077.35		$1,196.1202	$1,196.11	$1,196.15	$1,196.00