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	$86.29	3.306%	$89.1427	$89.14	$89.15	$89.10
Purchase #2	$108.31	9.572%	$118.6774	$118.68	$118.70	$118.70
Purchase #3	$81.47	12.316%	$91.5038	$91.50	$91.50	$91.50
Purchase #4	$39.44	8.190%	$42.6701	$42.67	$42.65	$42.70
Purchase #5	$51.93	3.854%	$53.9314	$53.93	$53.95	$53.90
Purchase #6	$242.98	12.435%	$273.1946	$273.19	$273.20	$273.20
Purchase #7	$52.89	11.227%	$58.828	$58.83	$58.85	$58.80
7 purchase totals =	$663.31		$727.9480	$727.94	$728.00	$727.90