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	$37.97	10.693%	$42.0301	$42.03	$42.05	$42.00
Purchase #2	$79.43	6.139%	$84.3062	$84.31	$84.30	$84.30
Purchase #3	$183.85	7.577%	$197.7803	$197.78	$197.80	$197.80
Purchase #4	$165.55	10.510%	$182.9493	$182.95	$182.95	$182.90
Purchase #5	$233.72	7.647%	$251.5926	$251.59	$251.60	$251.60
Purchase #6	$78.62	9.200%	$85.853	$85.85	$85.85	$85.90
Purchase #7	$144.35	9.763%	$158.4429	$158.44	$158.45	$158.40
7 purchase totals =	$923.49		$1,002.9544	$1,002.95	$1,003.00	$1,002.90