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	$249.90	3.543%	$258.754	$258.75	$258.75	$258.80
Purchase #2	$75.91	8.687%	$82.5043	$82.50	$82.50	$82.50
Purchase #3	$36.38	5.603%	$38.4184	$38.42	$38.40	$38.40
Purchase #4	$142.86	3.521%	$147.8901	$147.89	$147.90	$147.90
Purchase #5	$72.79	13.730%	$82.7841	$82.78	$82.80	$82.80
Purchase #6	$34.84	10.870%	$38.6271	$38.63	$38.65	$38.60
Purchase #7	$241.56	13.470%	$274.0981	$274.10	$274.10	$274.10
7 purchase totals =	$854.24		$923.0761	$923.07	$923.10	$923.10