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	$54.73	3.517%	$56.6549	$56.65	$56.65	$56.70
Purchase #2	$138.63	12.722%	$156.2665	$156.27	$156.25	$156.30
Purchase #3	$135.42	5.339%	$142.6501	$142.65	$142.65	$142.70
Purchase #4	$122.50	7.583%	$131.7892	$131.79	$131.80	$131.80
Purchase #5	$48.79	13.536%	$55.3942	$55.39	$55.40	$55.40
Purchase #6	$205.89	4.781%	$215.7336	$215.73	$215.75	$215.70
Purchase #7	$31.43	6.753%	$33.5525	$33.55	$33.55	$33.60
7 purchase totals =	$737.39		$792.0410	$792.03	$792.05	$792.20