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	$25.41	11.177%	$28.2501	$28.25	$28.25	$28.30
Purchase #2	$49.78	11.630%	$55.5694	$55.57	$55.55	$55.60
Purchase #3	$30.96	9.523%	$33.9083	$33.91	$33.90	$33.90
Purchase #4	$86.39	4.454%	$90.2378	$90.24	$90.25	$90.20
Purchase #5	$114.67	12.572%	$129.0863	$129.09	$129.10	$129.10
Purchase #6	$40.52	13.300%	$45.9092	$45.91	$45.90	$45.90
Purchase #7	$211.42	9.416%	$231.3273	$231.33	$231.35	$231.30
7 purchase totals =	$559.15		$614.2884	$614.30	$614.30	$614.30