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	$66.37	11.240%	$73.83	$73.83	$73.85	$73.80
Purchase #2	$249.36	8.389%	$270.2788	$270.28	$270.30	$270.30
Purchase #3	$113.59	8.365%	$123.0918	$123.09	$123.10	$123.10
Purchase #4	$43.44	3.691%	$45.0434	$45.04	$45.05	$45.00
Purchase #5	$216.85	8.273%	$234.79	$234.79	$234.80	$234.80
Purchase #6	$120.96	8.606%	$131.3698	$131.37	$131.35	$131.40
Purchase #7	$85.78	11.208%	$95.3942	$95.39	$95.40	$95.40
7 purchase totals =	$896.35		$973.7980	$973.79	$973.85	$973.80