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	$231.41	6.622%	$246.734	$246.73	$246.75	$246.70
Purchase #2	$187.61	6.124%	$199.0992	$199.10	$199.10	$199.10
Purchase #3	$209.82	13.611%	$238.3786	$238.38	$238.40	$238.40
Purchase #4	$120.39	6.789%	$128.5633	$128.56	$128.55	$128.60
Purchase #5	$178.54	12.226%	$200.3683	$200.37	$200.35	$200.40
Purchase #6	$65.66	10.711%	$72.6928	$72.69	$72.70	$72.70
Purchase #7	$93.70	11.260%	$104.2506	$104.25	$104.25	$104.30
7 purchase totals =	$1,087.13		$1,190.0868	$1,190.08	$1,190.10	$1,190.20