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	$233.75	9.686%	$256.391	$256.39	$256.40	$256.40
Purchase #2	$123.56	10.790%	$136.8921	$136.89	$136.90	$136.90
Purchase #3	$248.52	9.331%	$271.7094	$271.71	$271.70	$271.70
Purchase #4	$204.59	3.534%	$211.8202	$211.82	$211.80	$211.80
Purchase #5	$94.46	13.783%	$107.4794	$107.48	$107.50	$107.50
Purchase #6	$84.54	11.156%	$93.9713	$93.97	$93.95	$94.00
Purchase #7	$97.41	3.324%	$100.6479	$100.65	$100.65	$100.60
7 purchase totals =	$1,086.83		$1,178.9113	$1,178.91	$1,178.90	$1,178.90