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	$107.86	11.148%	$119.8842	$119.88	$119.90	$119.90
Purchase #2	$47.64	4.695%	$49.8767	$49.88	$49.90	$49.90
Purchase #3	$92.37	11.787%	$103.2577	$103.26	$103.25	$103.30
Purchase #4	$216.30	6.283%	$229.8901	$229.89	$229.90	$229.90
Purchase #5	$227.48	11.481%	$253.597	$253.60	$253.60	$253.60
Purchase #6	$27.56	8.238%	$29.8304	$29.83	$29.85	$29.80
Purchase #7	$103.68	7.581%	$111.54	$111.54	$111.55	$111.50
7 purchase totals =	$822.89		$897.8761	$897.88	$897.95	$897.90