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	$16.56	8.770%	$18.0123	$18.01	$18.00	$18.00
Purchase #2	$91.34	11.230%	$101.5975	$101.60	$101.60	$101.60
Purchase #3	$172.72	13.871%	$196.678	$196.68	$196.70	$196.70
Purchase #4	$131.98	10.689%	$146.0873	$146.09	$146.10	$146.10
Purchase #5	$208.95	3.518%	$216.3009	$216.30	$216.30	$216.30
Purchase #6	$186.41	12.414%	$209.5509	$209.55	$209.55	$209.60
Purchase #7	$196.47	13.591%	$223.1722	$223.17	$223.15	$223.20
7 purchase totals =	$1,004.43		$1,111.3991	$1,111.40	$1,111.40	$1,111.50