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	$205.50	12.672%	$231.541	$231.54	$231.55	$231.50
Purchase #2	$158.55	13.458%	$179.8877	$179.89	$179.90	$179.90
Purchase #3	$135.41	13.165%	$153.2367	$153.24	$153.25	$153.20
Purchase #4	$219.46	13.717%	$249.5633	$249.56	$249.55	$249.60
Purchase #5	$189.42	5.811%	$200.4272	$200.43	$200.45	$200.40
Purchase #6	$40.61	6.857%	$43.3946	$43.39	$43.40	$43.40
Purchase #7	$212.56	8.336%	$230.279	$230.28	$230.30	$230.30
7 purchase totals =	$1,161.51		$1,288.3295	$1,288.33	$1,288.40	$1,288.30