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	$243.87	11.269%	$271.3517	$271.35	$271.35	$271.40
Purchase #2	$190.90	7.492%	$205.2022	$205.20	$205.20	$205.20
Purchase #3	$180.32	8.850%	$196.2783	$196.28	$196.30	$196.30
Purchase #4	$69.85	12.830%	$78.8118	$78.81	$78.80	$78.80
Purchase #5	$173.40	5.257%	$182.5156	$182.52	$182.50	$182.50
Purchase #6	$55.29	3.551%	$57.2533	$57.25	$57.25	$57.30
Purchase #7	$50.47	13.699%	$57.3839	$57.38	$57.40	$57.40
7 purchase totals =	$964.10		$1,048.7968	$1,048.79	$1,048.80	$1,048.90