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	$56.55	7.380%	$60.7234	$60.72	$60.70	$60.70
Purchase #2	$137.78	9.844%	$151.3431	$151.34	$151.35	$151.30
Purchase #3	$18.60	12.854%	$20.9908	$20.99	$21.00	$21.00
Purchase #4	$54.86	8.726%	$59.6471	$59.65	$59.65	$59.60
Purchase #5	$236.59	9.699%	$259.5369	$259.54	$259.55	$259.50
Purchase #6	$170.77	6.796%	$182.3755	$182.38	$182.40	$182.40
Purchase #7	$185.65	3.341%	$191.8526	$191.85	$191.85	$191.90
7 purchase totals =	$860.80		$926.4694	$926.47	$926.50	$926.40