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	$18.37	12.605%	$20.6855	$20.69	$20.70	$20.70
Purchase #2	$178.48	12.430%	$200.6651	$200.67	$200.65	$200.70
Purchase #3	$134.32	12.601%	$151.2457	$151.25	$151.25	$151.20
Purchase #4	$189.84	7.728%	$204.5108	$204.51	$204.50	$204.50
Purchase #5	$49.43	5.512%	$52.1546	$52.15	$52.15	$52.20
Purchase #6	$71.87	5.182%	$75.5943	$75.59	$75.60	$75.60
Purchase #7	$141.96	10.102%	$156.3008	$156.30	$156.30	$156.30
7 purchase totals =	$784.27		$861.1568	$861.16	$861.15	$861.20