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	$40.32	4.409%	$42.0977	$42.10	$42.10	$42.10
Purchase #2	$160.88	7.342%	$172.6918	$172.69	$172.70	$172.70
Purchase #3	$37.47	9.180%	$40.9097	$40.91	$40.90	$40.90
Purchase #4	$198.65	5.380%	$209.3374	$209.34	$209.35	$209.30
Purchase #5	$167.65	4.653%	$175.4508	$175.45	$175.45	$175.50
Purchase #6	$59.28	5.861%	$62.7544	$62.75	$62.75	$62.80
Purchase #7	$115.67	6.164%	$122.7999	$122.80	$122.80	$122.80
7 purchase totals =	$779.92		$826.0417	$826.04	$826.05	$826.10