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	$71.82	10.428%	$79.3094	$79.31	$79.30	$79.30
Purchase #2	$111.34	7.119%	$119.2663	$119.27	$119.25	$119.30
Purchase #3	$71.90	8.616%	$78.0949	$78.09	$78.10	$78.10
Purchase #4	$100.43	5.442%	$105.8954	$105.90	$105.90	$105.90
Purchase #5	$59.30	5.424%	$62.5164	$62.52	$62.50	$62.50
Purchase #6	$212.98	3.370%	$220.1574	$220.16	$220.15	$220.20
Purchase #7	$118.51	13.650%	$134.6866	$134.69	$134.70	$134.70
7 purchase totals =	$746.28		$799.9264	$799.94	$799.90	$800.00