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	$41.40	4.738%	$43.3615	$43.36	$43.35	$43.40
Purchase #2	$22.48	10.669%	$24.8784	$24.88	$24.90	$24.90
Purchase #3	$228.36	8.197%	$247.0787	$247.08	$247.10	$247.10
Purchase #4	$33.73	10.141%	$37.1506	$37.15	$37.15	$37.20
Purchase #5	$38.28	5.871%	$40.5274	$40.53	$40.55	$40.50
Purchase #6	$165.53	9.767%	$181.6973	$181.70	$181.70	$181.70
Purchase #7	$59.57	11.682%	$66.529	$66.53	$66.55	$66.50
7 purchase totals =	$589.35		$641.2229	$641.23	$641.30	$641.30