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	$118.76	8.436%	$128.7786	$128.78	$128.80	$128.80
Purchase #2	$33.29	13.639%	$37.8304	$37.83	$37.85	$37.80
Purchase #3	$186.90	7.367%	$200.6689	$200.67	$200.65	$200.70
Purchase #4	$109.32	12.775%	$123.2856	$123.29	$123.30	$123.30
Purchase #5	$216.53	3.245%	$223.5564	$223.56	$223.55	$223.60
Purchase #6	$219.86	5.683%	$232.3546	$232.35	$232.35	$232.40
Purchase #7	$44.79	12.105%	$50.2118	$50.21	$50.20	$50.20
7 purchase totals =	$929.45		$996.6863	$996.69	$996.70	$996.80