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	$82.49	13.131%	$93.3218	$93.32	$93.30	$93.30
Purchase #2	$242.30	3.392%	$250.5188	$250.52	$250.50	$250.50
Purchase #3	$84.31	7.807%	$90.8921	$90.89	$90.90	$90.90
Purchase #4	$11.44	3.621%	$11.8542	$11.85	$11.85	$11.90
Purchase #5	$13.47	7.196%	$14.4393	$14.44	$14.45	$14.40
Purchase #6	$135.57	6.702%	$144.6559	$144.66	$144.65	$144.70
Purchase #7	$229.53	12.724%	$258.7354	$258.74	$258.75	$258.70
7 purchase totals =	$799.11		$864.4175	$864.42	$864.40	$864.40