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	$241.62	13.143%	$273.3761	$273.38	$273.40	$273.40
Purchase #2	$127.93	12.150%	$143.4735	$143.47	$143.45	$143.50
Purchase #3	$96.91	3.765%	$100.5587	$100.56	$100.55	$100.60
Purchase #4	$13.29	4.252%	$13.8551	$13.86	$13.85	$13.90
Purchase #5	$183.71	13.706%	$208.8893	$208.89	$208.90	$208.90
Purchase #6	$245.37	9.289%	$268.1624	$268.16	$268.15	$268.20
Purchase #7	$229.30	12.129%	$257.1118	$257.11	$257.10	$257.10
7 purchase totals =	$1,138.13		$1,265.4269	$1,265.43	$1,265.40	$1,265.60