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	$84.88	6.334%	$90.2563	$90.26	$90.25	$90.30
Purchase #2	$52.95	5.708%	$55.9724	$55.97	$55.95	$56.00
Purchase #3	$230.98	3.266%	$238.5238	$238.52	$238.50	$238.50
Purchase #4	$171.80	10.811%	$190.3733	$190.37	$190.35	$190.40
Purchase #5	$175.80	11.574%	$196.1471	$196.15	$196.15	$196.10
Purchase #6	$81.66	4.426%	$85.2743	$85.27	$85.25	$85.30
Purchase #7	$246.44	6.426%	$262.2762	$262.28	$262.30	$262.30
7 purchase totals =	$1,044.51		$1,118.8234	$1,118.82	$1,118.75	$1,118.90