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	$228.52	9.263%	$249.6878	$249.69	$249.70	$249.70
Purchase #2	$247.43	9.453%	$270.8196	$270.82	$270.80	$270.80
Purchase #3	$130.89	6.212%	$139.0209	$139.02	$139.00	$139.00
Purchase #4	$67.98	5.422%	$71.6659	$71.67	$71.65	$71.70
Purchase #5	$19.48	4.656%	$20.387	$20.39	$20.40	$20.40
Purchase #6	$122.39	7.215%	$131.2204	$131.22	$131.20	$131.20
Purchase #7	$113.53	3.740%	$117.776	$117.78	$117.80	$117.80
7 purchase totals =	$930.22		$1,000.5776	$1,000.59	$1,000.55	$1,000.60