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	$72.29	7.757%	$77.8975	$77.90	$77.90	$77.90
Purchase #2	$81.80	11.362%	$91.0941	$91.09	$91.10	$91.10
Purchase #3	$195.41	5.273%	$205.714	$205.71	$205.70	$205.70
Purchase #4	$102.72	12.543%	$115.6042	$115.60	$115.60	$115.60
Purchase #5	$72.66	13.780%	$82.6725	$82.67	$82.65	$82.70
Purchase #6	$81.78	4.705%	$85.6277	$85.63	$85.65	$85.60
Purchase #7	$137.39	9.622%	$150.6097	$150.61	$150.60	$150.60
7 purchase totals =	$744.05		$809.2197	$809.21	$809.20	$809.20