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	$137.40	4.341%	$143.3645	$143.36	$143.35	$143.40
Purchase #2	$37.48	6.241%	$39.8191	$39.82	$39.80	$39.80
Purchase #3	$221.27	10.776%	$245.1141	$245.11	$245.10	$245.10
Purchase #4	$109.46	8.752%	$119.0399	$119.04	$119.05	$119.00
Purchase #5	$40.42	13.171%	$45.7437	$45.74	$45.75	$45.70
Purchase #6	$233.32	13.615%	$265.0865	$265.09	$265.10	$265.10
Purchase #7	$37.48	10.294%	$41.3382	$41.34	$41.35	$41.30
7 purchase totals =	$816.83		$899.5060	$899.50	$899.50	$899.40