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	$229.95	10.657%	$254.4558	$254.46	$254.45	$254.50
Purchase #2	$20.40	5.400%	$21.5016	$21.50	$21.50	$21.50
Purchase #3	$19.91	4.444%	$20.7948	$20.79	$20.80	$20.80
Purchase #4	$83.91	4.127%	$87.373	$87.37	$87.35	$87.40
Purchase #5	$168.42	12.799%	$189.9761	$189.98	$190.00	$190.00
Purchase #6	$97.29	6.474%	$103.5886	$103.59	$103.60	$103.60
Purchase #7	$136.92	13.359%	$155.2111	$155.21	$155.20	$155.20
7 purchase totals =	$756.80		$832.9010	$832.90	$832.90	$833.00