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	$48.71	3.610%	$50.4684	$50.47	$50.45	$50.50
Purchase #2	$83.88	7.763%	$90.3916	$90.39	$90.40	$90.40
Purchase #3	$112.39	4.502%	$117.4498	$117.45	$117.45	$117.40
Purchase #4	$198.50	8.279%	$214.9338	$214.93	$214.95	$214.90
Purchase #5	$176.66	8.630%	$191.9058	$191.91	$191.90	$191.90
Purchase #6	$42.40	5.275%	$44.6366	$44.64	$44.65	$44.60
Purchase #7	$130.33	13.661%	$148.1344	$148.13	$148.15	$148.10
7 purchase totals =	$792.87		$857.9204	$857.92	$857.95	$857.80