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	$87.48	5.571%	$92.3535	$92.35	$92.35	$92.40
Purchase #2	$130.86	10.334%	$144.3831	$144.38	$144.40	$144.40
Purchase #3	$124.50	4.330%	$129.8909	$129.89	$129.90	$129.90
Purchase #4	$96.37	4.379%	$100.59	$100.59	$100.60	$100.60
Purchase #5	$160.32	5.403%	$168.9821	$168.98	$169.00	$169.00
Purchase #6	$245.25	13.487%	$278.3269	$278.33	$278.35	$278.30
Purchase #7	$5.33	3.139%	$5.4973	$5.50	$5.50	$5.50
7 purchase totals =	$850.11		$920.0238	$920.02	$920.10	$920.10