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	$168.62	8.812%	$183.4788	$183.48	$183.50	$183.50
Purchase #2	$126.65	3.853%	$131.5298	$131.53	$131.55	$131.50
Purchase #3	$149.37	10.237%	$164.661	$164.66	$164.65	$164.70
Purchase #4	$149.46	4.139%	$155.6461	$155.65	$155.65	$155.60
Purchase #5	$248.60	12.690%	$280.1473	$280.15	$280.15	$280.10
Purchase #6	$42.26	10.175%	$46.56	$46.56	$46.55	$46.60
Purchase #7	$206.91	4.643%	$216.5168	$216.52	$216.50	$216.50
7 purchase totals =	$1,091.87		$1,178.5398	$1,178.55	$1,178.55	$1,178.50