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	$37.53	12.164%	$42.0951	$42.10	$42.10	$42.10
Purchase #2	$25.52	12.174%	$28.6268	$28.63	$28.65	$28.60
Purchase #3	$167.74	12.369%	$188.4878	$188.49	$188.50	$188.50
Purchase #4	$179.33	13.745%	$203.9789	$203.98	$204.00	$204.00
Purchase #5	$205.52	8.394%	$222.7713	$222.77	$222.75	$222.80
Purchase #6	$155.59	4.409%	$162.45	$162.45	$162.45	$162.50
Purchase #7	$177.74	9.795%	$195.1496	$195.15	$195.15	$195.10
7 purchase totals =	$948.97		$1,043.5595	$1,043.57	$1,043.60	$1,043.60