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	$129.38	6.532%	$137.8311	$137.83	$137.85	$137.80
Purchase #2	$99.44	6.285%	$105.6898	$105.69	$105.70	$105.70
Purchase #3	$44.47	9.497%	$48.6933	$48.69	$48.70	$48.70
Purchase #4	$25.88	5.377%	$27.2716	$27.27	$27.25	$27.30
Purchase #5	$196.40	9.636%	$215.3251	$215.33	$215.35	$215.30
Purchase #6	$240.39	8.311%	$260.3688	$260.37	$260.35	$260.40
Purchase #7	$76.82	9.187%	$83.8775	$83.88	$83.90	$83.90
7 purchase totals =	$812.78		$879.0572	$879.06	$879.10	$879.10