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	$36.41	12.243%	$40.8677	$40.87	$40.85	$40.90
Purchase #2	$111.88	10.412%	$123.5289	$123.53	$123.55	$123.50
Purchase #3	$230.37	10.261%	$254.0083	$254.01	$254.00	$254.00
Purchase #4	$211.96	3.742%	$219.8915	$219.89	$219.90	$219.90
Purchase #5	$96.77	6.457%	$103.0184	$103.02	$103.00	$103.00
Purchase #6	$79.81	4.436%	$83.3504	$83.35	$83.35	$83.40
Purchase #7	$88.40	5.446%	$93.2143	$93.21	$93.20	$93.20
7 purchase totals =	$855.60		$917.8795	$917.88	$917.85	$917.90