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	$79.38	3.844%	$82.4314	$82.43	$82.45	$82.40
Purchase #2	$183.36	8.769%	$199.4388	$199.44	$199.45	$199.40
Purchase #3	$114.39	11.265%	$127.276	$127.28	$127.30	$127.30
Purchase #4	$65.44	4.634%	$68.4725	$68.47	$68.45	$68.50
Purchase #5	$186.69	13.287%	$211.4955	$211.50	$211.50	$211.50
Purchase #6	$35.61	11.644%	$39.7564	$39.76	$39.75	$39.80
Purchase #7	$78.85	5.289%	$83.0204	$83.02	$83.00	$83.00
7 purchase totals =	$743.72		$811.8910	$811.90	$811.90	$811.90