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	$141.49	3.350%	$146.2299	$146.23	$146.25	$146.20
Purchase #2	$28.60	9.582%	$31.3405	$31.34	$31.35	$31.30
Purchase #3	$31.84	6.437%	$33.8895	$33.89	$33.90	$33.90
Purchase #4	$73.47	12.416%	$82.592	$82.59	$82.60	$82.60
Purchase #5	$59.55	7.265%	$63.8763	$63.88	$63.90	$63.90
Purchase #6	$132.91	9.412%	$145.4195	$145.42	$145.40	$145.40
Purchase #7	$43.30	11.668%	$48.3522	$48.35	$48.35	$48.40
7 purchase totals =	$511.16		$551.6999	$551.70	$551.75	$551.70