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	$248.45	12.586%	$279.7199	$279.72	$279.70	$279.70
Purchase #2	$112.96	3.487%	$116.8989	$116.90	$116.90	$116.90
Purchase #3	$83.78	6.759%	$89.4427	$89.44	$89.45	$89.40
Purchase #4	$84.40	3.303%	$87.1877	$87.19	$87.20	$87.20
Purchase #5	$9.32	11.626%	$10.4035	$10.40	$10.40	$10.40
Purchase #6	$42.35	7.577%	$45.5589	$45.56	$45.55	$45.60
Purchase #7	$209.41	10.746%	$231.9132	$231.91	$231.90	$231.90
7 purchase totals =	$790.67		$861.1248	$861.12	$861.10	$861.10