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	$236.56	4.386%	$246.9355	$246.94	$246.95	$246.90
Purchase #2	$233.59	6.871%	$249.64	$249.64	$249.65	$249.60
Purchase #3	$69.86	3.821%	$72.5294	$72.53	$72.55	$72.50
Purchase #4	$140.41	7.747%	$151.2876	$151.29	$151.30	$151.30
Purchase #5	$72.55	8.650%	$78.8256	$78.83	$78.85	$78.80
Purchase #6	$9.73	11.167%	$10.8165	$10.82	$10.80	$10.80
Purchase #7	$176.32	7.316%	$189.2196	$189.22	$189.20	$189.20
7 purchase totals =	$939.02		$999.2542	$999.27	$999.30	$999.10