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	$123.29	6.237%	$130.9796	$130.98	$131.00	$131.00
Purchase #2	$238.60	11.638%	$266.3683	$266.37	$266.35	$266.40
Purchase #3	$228.46	8.590%	$248.0847	$248.08	$248.10	$248.10
Purchase #4	$151.83	10.519%	$167.801	$167.80	$167.80	$167.80
Purchase #5	$42.67	11.628%	$47.6317	$47.63	$47.65	$47.60
Purchase #6	$55.95	6.497%	$59.5851	$59.59	$59.60	$59.60
Purchase #7	$31.68	13.802%	$36.0525	$36.05	$36.05	$36.10
7 purchase totals =	$872.48		$956.5029	$956.50	$956.55	$956.60