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	$19.59	10.113%	$21.5711	$21.57	$21.55	$21.60
Purchase #2	$33.81	7.276%	$36.27	$36.27	$36.25	$36.30
Purchase #3	$241.71	9.824%	$265.4556	$265.46	$265.45	$265.50
Purchase #4	$181.45	6.425%	$193.1082	$193.11	$193.10	$193.10
Purchase #5	$82.97	10.105%	$91.3541	$91.35	$91.35	$91.40
Purchase #6	$99.61	11.686%	$111.2504	$111.25	$111.25	$111.30
Purchase #7	$131.87	11.150%	$146.5735	$146.57	$146.55	$146.60
7 purchase totals =	$791.01		$865.5829	$865.58	$865.50	$865.80