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	$35.45	10.632%	$39.219	$39.22	$39.20	$39.20
Purchase #2	$156.59	11.408%	$174.4538	$174.45	$174.45	$174.50
Purchase #3	$70.34	3.630%	$72.8933	$72.89	$72.90	$72.90
Purchase #4	$128.61	5.571%	$135.7749	$135.77	$135.75	$135.80
Purchase #5	$132.71	5.730%	$140.3143	$140.31	$140.30	$140.30
Purchase #6	$130.29	3.504%	$134.8554	$134.86	$134.85	$134.90
Purchase #7	$45.90	7.343%	$49.2704	$49.27	$49.25	$49.30
7 purchase totals =	$699.89		$746.7811	$746.77	$746.70	$746.90