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	$185.38	8.328%	$200.8184	$200.82	$200.80	$200.80
Purchase #2	$164.96	9.635%	$180.8539	$180.85	$180.85	$180.90
Purchase #3	$231.73	11.385%	$258.1125	$258.11	$258.10	$258.10
Purchase #4	$179.47	10.425%	$198.1797	$198.18	$198.20	$198.20
Purchase #5	$159.65	7.381%	$171.4338	$171.43	$171.45	$171.40
Purchase #6	$76.34	7.722%	$82.235	$82.24	$82.25	$82.20
Purchase #7	$217.89	9.384%	$238.3368	$238.34	$238.35	$238.30
7 purchase totals =	$1,215.42		$1,329.9701	$1,329.97	$1,330.00	$1,329.90