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	$33.75	11.534%	$37.6427	$37.64	$37.65	$37.60
Purchase #2	$196.65	6.160%	$208.7636	$208.76	$208.75	$208.80
Purchase #3	$168.30	12.490%	$189.3207	$189.32	$189.30	$189.30
Purchase #4	$217.38	10.520%	$240.2484	$240.25	$240.25	$240.20
Purchase #5	$104.33	8.110%	$112.7912	$112.79	$112.80	$112.80
Purchase #6	$63.82	13.677%	$72.5487	$72.55	$72.55	$72.50
Purchase #7	$48.56	7.845%	$52.3695	$52.37	$52.35	$52.40
7 purchase totals =	$832.79		$913.6848	$913.68	$913.65	$913.60