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	$37.34	13.719%	$42.4627	$42.46	$42.45	$42.50
Purchase #2	$103.54	9.507%	$113.3835	$113.38	$113.40	$113.40
Purchase #3	$68.69	8.526%	$74.5465	$74.55	$74.55	$74.50
Purchase #4	$143.27	6.370%	$152.3963	$152.40	$152.40	$152.40
Purchase #5	$38.29	3.179%	$39.5072	$39.51	$39.50	$39.50
Purchase #6	$205.34	12.614%	$231.2416	$231.24	$231.25	$231.20
Purchase #7	$111.95	7.231%	$120.0451	$120.05	$120.05	$120.00
7 purchase totals =	$708.42		$773.5829	$773.59	$773.60	$773.50