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	$166.76	13.662%	$189.5428	$189.54	$189.55	$189.50
Purchase #2	$104.57	10.342%	$115.3846	$115.38	$115.40	$115.40
Purchase #3	$169.70	6.338%	$180.4556	$180.46	$180.45	$180.50
Purchase #4	$164.56	9.507%	$180.2047	$180.20	$180.20	$180.20
Purchase #5	$37.71	6.664%	$40.223	$40.22	$40.20	$40.20
Purchase #6	$52.54	3.216%	$54.2297	$54.23	$54.25	$54.20
Purchase #7	$221.60	13.441%	$251.3853	$251.39	$251.40	$251.40
7 purchase totals =	$917.44		$1,011.4257	$1,011.42	$1,011.45	$1,011.40