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	$90.41	5.714%	$95.576	$95.58	$95.60	$95.60
Purchase #2	$69.41	12.570%	$78.1348	$78.13	$78.15	$78.10
Purchase #3	$157.80	12.466%	$177.4713	$177.47	$177.45	$177.50
Purchase #4	$71.89	3.541%	$74.4356	$74.44	$74.45	$74.40
Purchase #5	$249.26	11.686%	$278.3885	$278.39	$278.40	$278.40
Purchase #6	$59.96	7.633%	$64.5367	$64.54	$64.55	$64.50
Purchase #7	$67.60	5.466%	$71.295	$71.30	$71.30	$71.30
7 purchase totals =	$766.33		$839.8379	$839.85	$839.90	$839.80