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	$236.59	7.824%	$255.1008	$255.10	$255.10	$255.10
Purchase #2	$39.91	11.828%	$44.6306	$44.63	$44.65	$44.60
Purchase #3	$172.37	9.585%	$188.8917	$188.89	$188.90	$188.90
Purchase #4	$181.41	13.449%	$205.8078	$205.81	$205.80	$205.80
Purchase #5	$73.30	6.434%	$78.0161	$78.02	$78.00	$78.00
Purchase #6	$198.88	10.434%	$219.6311	$219.63	$219.65	$219.60
Purchase #7	$44.70	9.314%	$48.8634	$48.86	$48.85	$48.90
7 purchase totals =	$947.16		$1,040.9415	$1,040.94	$1,040.95	$1,040.90