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	$233.67	10.802%	$258.911	$258.91	$258.90	$258.90
Purchase #2	$179.84	13.574%	$204.2515	$204.25	$204.25	$204.30
Purchase #3	$27.54	11.572%	$30.7269	$30.73	$30.75	$30.70
Purchase #4	$123.92	3.540%	$128.3068	$128.31	$128.30	$128.30
Purchase #5	$45.72	11.224%	$50.8516	$50.85	$50.85	$50.90
Purchase #6	$137.79	6.360%	$146.5534	$146.55	$146.55	$146.60
Purchase #7	$150.90	11.377%	$168.0679	$168.07	$168.05	$168.10
7 purchase totals =	$899.38		$987.6691	$987.67	$987.65	$987.80