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	$16.82	9.118%	$18.3536	$18.35	$18.35	$18.40
Purchase #2	$79.71	3.370%	$82.3962	$82.40	$82.40	$82.40
Purchase #3	$27.82	6.285%	$29.5685	$29.57	$29.55	$29.60
Purchase #4	$46.77	8.787%	$50.8797	$50.88	$50.90	$50.90
Purchase #5	$156.99	6.715%	$167.5319	$167.53	$167.55	$167.50
Purchase #6	$133.34	5.843%	$141.1311	$141.13	$141.15	$141.10
Purchase #7	$76.41	7.340%	$82.0185	$82.02	$82.00	$82.00
7 purchase totals =	$537.86		$571.8795	$571.88	$571.90	$571.90