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	$21.57	4.273%	$22.4917	$22.49	$22.50	$22.50
Purchase #2	$72.81	13.402%	$82.568	$82.57	$82.55	$82.60
Purchase #3	$193.53	7.696%	$208.4241	$208.42	$208.40	$208.40
Purchase #4	$82.43	7.832%	$88.8859	$88.89	$88.90	$88.90
Purchase #5	$133.47	9.445%	$146.0762	$146.08	$146.10	$146.10
Purchase #6	$40.69	9.709%	$44.6406	$44.64	$44.65	$44.60
Purchase #7	$178.81	5.827%	$189.2293	$189.23	$189.25	$189.20
7 purchase totals =	$723.31		$782.3158	$782.32	$782.35	$782.30