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	$250.93	11.394%	$279.521	$279.52	$279.50	$279.50
Purchase #2	$181.93	8.439%	$197.2831	$197.28	$197.30	$197.30
Purchase #3	$224.37	9.571%	$245.8445	$245.84	$245.85	$245.80
Purchase #4	$142.57	3.510%	$147.5742	$147.57	$147.55	$147.60
Purchase #5	$169.46	6.124%	$179.8377	$179.84	$179.85	$179.80
Purchase #6	$53.96	7.520%	$58.0178	$58.02	$58.00	$58.00
Purchase #7	$85.47	3.329%	$88.3153	$88.32	$88.30	$88.30
7 purchase totals =	$1,108.69		$1,196.3936	$1,196.39	$1,196.35	$1,196.30