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	$159.32	9.517%	$174.4825	$174.48	$174.50	$174.50
Purchase #2	$167.51	6.446%	$178.3077	$178.31	$178.30	$178.30
Purchase #3	$114.63	12.466%	$128.9198	$128.92	$128.90	$128.90
Purchase #4	$75.48	8.768%	$82.0981	$82.10	$82.10	$82.10
Purchase #5	$89.39	12.832%	$100.8605	$100.86	$100.85	$100.90
Purchase #6	$6.97	6.704%	$7.4373	$7.44	$7.45	$7.40
Purchase #7	$101.98	10.449%	$112.6359	$112.64	$112.65	$112.60
7 purchase totals =	$715.28		$784.7418	$784.75	$784.75	$784.70