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	$52.38	7.293%	$56.2001	$56.20	$56.20	$56.20
Purchase #2	$81.59	10.271%	$89.9701	$89.97	$89.95	$90.00
Purchase #3	$222.39	12.390%	$249.9441	$249.94	$249.95	$249.90
Purchase #4	$106.33	5.828%	$112.5269	$112.53	$112.55	$112.50
Purchase #5	$152.84	10.251%	$168.5076	$168.51	$168.50	$168.50
Purchase #6	$165.68	13.854%	$188.6333	$188.63	$188.65	$188.60
Purchase #7	$120.70	5.780%	$127.6765	$127.68	$127.70	$127.70
7 purchase totals =	$901.91		$993.4586	$993.46	$993.50	$993.40