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	$23.57	10.437%	$26.03	$26.03	$26.05	$26.00
Purchase #2	$40.51	3.820%	$42.0575	$42.06	$42.05	$42.10
Purchase #3	$34.77	10.175%	$38.3078	$38.31	$38.30	$38.30
Purchase #4	$192.89	13.407%	$218.7508	$218.75	$218.75	$218.80
Purchase #5	$133.85	10.369%	$147.7289	$147.73	$147.75	$147.70
Purchase #6	$72.88	8.276%	$78.9115	$78.91	$78.90	$78.90
Purchase #7	$16.82	8.342%	$18.2231	$18.22	$18.20	$18.20
7 purchase totals =	$515.29		$570.0096	$570.01	$570.00	$570.00