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	$129.36	5.158%	$136.0324	$136.03	$136.05	$136.00
Purchase #2	$102.30	8.857%	$111.3607	$111.36	$111.35	$111.40
Purchase #3	$155.63	8.457%	$168.7916	$168.79	$168.80	$168.80
Purchase #4	$10.43	10.599%	$11.5355	$11.54	$11.55	$11.50
Purchase #5	$201.50	8.356%	$218.3373	$218.34	$218.35	$218.30
Purchase #6	$196.92	13.132%	$222.7795	$222.78	$222.80	$222.80
Purchase #7	$13.84	13.252%	$15.6741	$15.67	$15.65	$15.70
7 purchase totals =	$809.98		$884.5111	$884.51	$884.55	$884.50