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	$113.90	12.535%	$128.1774	$128.18	$128.20	$128.20
Purchase #2	$249.41	10.323%	$275.1566	$275.16	$275.15	$275.20
Purchase #3	$115.52	13.494%	$131.1083	$131.11	$131.10	$131.10
Purchase #4	$68.91	12.134%	$77.2715	$77.27	$77.25	$77.30
Purchase #5	$119.43	12.566%	$134.4376	$134.44	$134.45	$134.40
Purchase #6	$124.87	5.634%	$131.9052	$131.91	$131.90	$131.90
Purchase #7	$64.65	12.769%	$72.9052	$72.91	$72.90	$72.90
7 purchase totals =	$856.69		$950.9618	$950.98	$950.95	$951.00