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	$54.26	13.184%	$61.4136	$61.41	$61.40	$61.40
Purchase #2	$144.84	10.777%	$160.4494	$160.45	$160.45	$160.40
Purchase #3	$41.32	5.260%	$43.4934	$43.49	$43.50	$43.50
Purchase #4	$132.82	6.606%	$141.5941	$141.59	$141.60	$141.60
Purchase #5	$167.34	4.842%	$175.4426	$175.44	$175.45	$175.40
Purchase #6	$64.53	7.300%	$69.2407	$69.24	$69.25	$69.20
Purchase #7	$147.99	13.860%	$168.5014	$168.50	$168.50	$168.50
7 purchase totals =	$753.10		$820.1352	$820.12	$820.15	$820.00