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	$85.50	6.271%	$90.8617	$90.86	$90.85	$90.90
Purchase #2	$47.87	9.155%	$52.2525	$52.25	$52.25	$52.30
Purchase #3	$208.61	6.140%	$221.4187	$221.42	$221.40	$221.40
Purchase #4	$202.35	8.786%	$220.1285	$220.13	$220.15	$220.10
Purchase #5	$164.57	9.166%	$179.6545	$179.65	$179.65	$179.70
Purchase #6	$90.40	9.324%	$98.8289	$98.83	$98.85	$98.80
Purchase #7	$65.72	11.361%	$73.1864	$73.19	$73.20	$73.20
7 purchase totals =	$865.02		$936.3312	$936.33	$936.35	$936.40