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	$17.92	12.538%	$20.1668	$20.17	$20.15	$20.20
Purchase #2	$167.95	9.842%	$184.4796	$184.48	$184.50	$184.50
Purchase #3	$6.69	12.655%	$7.5366	$7.54	$7.55	$7.50
Purchase #4	$213.93	10.475%	$236.3392	$236.34	$236.35	$236.30
Purchase #5	$158.58	6.469%	$168.8385	$168.84	$168.85	$168.80
Purchase #6	$171.99	4.429%	$179.6074	$179.61	$179.60	$179.60
Purchase #7	$112.48	10.120%	$123.863	$123.86	$123.85	$123.90
7 purchase totals =	$849.54		$920.8311	$920.84	$920.85	$920.80