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	$122.79	10.851%	$136.1139	$136.11	$136.10	$136.10
Purchase #2	$52.38	13.532%	$59.4681	$59.47	$59.45	$59.50
Purchase #3	$35.39	5.648%	$37.3888	$37.39	$37.40	$37.40
Purchase #4	$172.78	9.640%	$189.436	$189.44	$189.45	$189.40
Purchase #5	$235.33	4.142%	$245.0774	$245.08	$245.10	$245.10
Purchase #6	$135.35	4.494%	$141.4326	$141.43	$141.45	$141.40
Purchase #7	$177.89	3.270%	$183.707	$183.71	$183.70	$183.70
7 purchase totals =	$931.91		$992.6238	$992.63	$992.65	$992.60