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	$103.31	6.362%	$109.8826	$109.88	$109.90	$109.90
Purchase #2	$247.76	4.396%	$258.6515	$258.65	$258.65	$258.70
Purchase #3	$131.36	4.445%	$137.199	$137.20	$137.20	$137.20
Purchase #4	$230.83	8.125%	$249.5849	$249.58	$249.60	$249.60
Purchase #5	$229.67	12.315%	$257.9539	$257.95	$257.95	$258.00
Purchase #6	$173.60	13.119%	$196.3746	$196.37	$196.35	$196.40
Purchase #7	$142.90	10.744%	$158.2532	$158.25	$158.25	$158.30
7 purchase totals =	$1,259.43		$1,367.8997	$1,367.88	$1,367.90	$1,368.10