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	$82.76	9.826%	$90.892	$90.89	$90.90	$90.90
Purchase #2	$34.43	13.656%	$39.1318	$39.13	$39.15	$39.10
Purchase #3	$65.60	11.821%	$73.3546	$73.35	$73.35	$73.40
Purchase #4	$162.92	11.763%	$182.0843	$182.08	$182.10	$182.10
Purchase #5	$56.47	6.392%	$60.0796	$60.08	$60.10	$60.10
Purchase #6	$31.39	13.373%	$35.5878	$35.59	$35.60	$35.60
Purchase #7	$41.31	6.680%	$44.0695	$44.07	$44.05	$44.10
7 purchase totals =	$474.88		$525.1996	$525.19	$525.25	$525.30