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	$37.79	11.777%	$42.2405	$42.24	$42.25	$42.20
Purchase #2	$153.42	12.578%	$172.7172	$172.72	$172.70	$172.70
Purchase #3	$208.90	12.173%	$234.3294	$234.33	$234.35	$234.30
Purchase #4	$55.61	3.386%	$57.493	$57.49	$57.50	$57.50
Purchase #5	$51.83	7.781%	$55.8629	$55.86	$55.85	$55.90
Purchase #6	$91.90	11.785%	$102.7304	$102.73	$102.75	$102.70
Purchase #7	$167.71	5.340%	$176.6657	$176.67	$176.65	$176.70
7 purchase totals =	$767.16		$842.0391	$842.04	$842.05	$842.00