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	$63.35	12.206%	$71.0825	$71.08	$71.10	$71.10
Purchase #2	$50.89	13.819%	$57.9225	$57.92	$57.90	$57.90
Purchase #3	$18.91	5.813%	$20.0092	$20.01	$20.00	$20.00
Purchase #4	$239.90	11.311%	$267.0351	$267.04	$267.05	$267.00
Purchase #5	$177.90	10.237%	$196.1116	$196.11	$196.10	$196.10
Purchase #6	$159.54	13.173%	$180.5562	$180.56	$180.55	$180.60
Purchase #7	$71.43	9.326%	$78.0916	$78.09	$78.10	$78.10
7 purchase totals =	$781.92		$870.8087	$870.81	$870.80	$870.80