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	$90.33	11.156%	$100.4072	$100.41	$100.40	$100.40
Purchase #2	$153.29	7.366%	$164.5813	$164.58	$164.60	$164.60
Purchase #3	$167.65	7.559%	$180.3227	$180.32	$180.30	$180.30
Purchase #4	$36.79	10.426%	$40.6257	$40.63	$40.65	$40.60
Purchase #5	$25.62	3.762%	$26.5838	$26.58	$26.60	$26.60
Purchase #6	$179.36	9.721%	$196.7956	$196.80	$196.80	$196.80
Purchase #7	$83.75	4.630%	$87.6276	$87.63	$87.65	$87.60
7 purchase totals =	$736.79		$796.9439	$796.95	$797.00	$796.90