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	$21.60	12.840%	$24.3734	$24.37	$24.35	$24.40
Purchase #2	$35.35	5.591%	$37.3264	$37.33	$37.35	$37.30
Purchase #3	$106.89	3.749%	$110.8973	$110.90	$110.90	$110.90
Purchase #4	$127.91	5.331%	$134.7289	$134.73	$134.75	$134.70
Purchase #5	$228.47	5.307%	$240.5949	$240.59	$240.60	$240.60
Purchase #6	$217.74	11.759%	$243.344	$243.34	$243.35	$243.30
Purchase #7	$214.31	5.125%	$225.2934	$225.29	$225.30	$225.30
7 purchase totals =	$952.27		$1,016.5583	$1,016.55	$1,016.60	$1,016.50