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	$123.57	8.323%	$133.8547	$133.85	$133.85	$133.90
Purchase #2	$100.34	10.168%	$110.5426	$110.54	$110.55	$110.50
Purchase #3	$64.28	6.401%	$68.3946	$68.39	$68.40	$68.40
Purchase #4	$198.76	5.490%	$209.6719	$209.67	$209.65	$209.70
Purchase #5	$53.90	10.333%	$59.4695	$59.47	$59.45	$59.50
Purchase #6	$230.54	6.713%	$246.0162	$246.02	$246.00	$246.00
Purchase #7	$82.95	11.484%	$92.476	$92.48	$92.50	$92.50
7 purchase totals =	$854.34		$920.4255	$920.42	$920.40	$920.50