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	$81.95	9.594%	$89.8123	$89.81	$89.80	$89.80
Purchase #2	$181.54	9.272%	$198.3724	$198.37	$198.35	$198.40
Purchase #3	$83.79	6.688%	$89.3939	$89.39	$89.40	$89.40
Purchase #4	$248.58	12.442%	$279.5083	$279.51	$279.50	$279.50
Purchase #5	$39.38	11.295%	$43.828	$43.83	$43.85	$43.80
Purchase #6	$107.87	5.424%	$113.7209	$113.72	$113.70	$113.70
Purchase #7	$41.57	3.126%	$42.8695	$42.87	$42.85	$42.90
7 purchase totals =	$784.68		$857.5053	$857.50	$857.45	$857.50