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	$55.46	4.871%	$58.1615	$58.16	$58.15	$58.20
Purchase #2	$196.55	12.604%	$221.3232	$221.32	$221.30	$221.30
Purchase #3	$131.66	9.482%	$144.144	$144.14	$144.15	$144.10
Purchase #4	$166.38	9.797%	$182.6802	$182.68	$182.70	$182.70
Purchase #5	$167.64	8.406%	$181.7318	$181.73	$181.75	$181.70
Purchase #6	$77.36	3.655%	$80.1875	$80.19	$80.20	$80.20
Purchase #7	$99.25	12.720%	$111.8746	$111.87	$111.85	$111.90
7 purchase totals =	$894.30		$980.1028	$980.09	$980.10	$980.10