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	$93.89	5.707%	$99.2483	$99.25	$99.25	$99.20
Purchase #2	$53.78	10.277%	$59.307	$59.31	$59.30	$59.30
Purchase #3	$21.28	10.741%	$23.5657	$23.57	$23.55	$23.60
Purchase #4	$147.35	9.138%	$160.8148	$160.81	$160.80	$160.80
Purchase #5	$43.74	9.856%	$48.051	$48.05	$48.05	$48.10
Purchase #6	$192.33	12.329%	$216.0424	$216.04	$216.05	$216.00
Purchase #7	$248.90	13.416%	$282.2924	$282.29	$282.30	$282.30
7 purchase totals =	$801.27		$889.3216	$889.32	$889.30	$889.30