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	$170.31	4.345%	$177.71	$177.71	$177.70	$177.70
Purchase #2	$65.79	7.607%	$70.7946	$70.79	$70.80	$70.80
Purchase #3	$59.48	12.716%	$67.0435	$67.04	$67.05	$67.00
Purchase #4	$122.81	4.484%	$128.3168	$128.32	$128.30	$128.30
Purchase #5	$59.96	6.375%	$63.7825	$63.78	$63.80	$63.80
Purchase #6	$72.36	13.858%	$82.3876	$82.39	$82.40	$82.40
Purchase #7	$137.74	9.236%	$150.4617	$150.46	$150.45	$150.50
7 purchase totals =	$688.45		$740.4967	$740.49	$740.50	$740.50