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	$70.82	13.439%	$80.3375	$80.34	$80.35	$80.30
Purchase #2	$123.27	9.340%	$134.7834	$134.78	$134.80	$134.80
Purchase #3	$92.68	5.771%	$98.0286	$98.03	$98.05	$98.00
Purchase #4	$84.43	3.776%	$87.6181	$87.62	$87.60	$87.60
Purchase #5	$167.75	10.625%	$185.5734	$185.57	$185.55	$185.60
Purchase #6	$88.55	7.857%	$95.5074	$95.51	$95.50	$95.50
Purchase #7	$196.87	11.474%	$219.4589	$219.46	$219.45	$219.50
7 purchase totals =	$824.37		$901.3073	$901.31	$901.30	$901.30