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	$138.62	3.303%	$143.1986	$143.20	$143.20	$143.20
Purchase #2	$37.43	12.231%	$42.0081	$42.01	$42.00	$42.00
Purchase #3	$71.97	9.653%	$78.9173	$78.92	$78.90	$78.90
Purchase #4	$41.84	3.316%	$43.2274	$43.23	$43.25	$43.20
Purchase #5	$16.35	13.410%	$18.5425	$18.54	$18.55	$18.50
Purchase #6	$141.98	5.824%	$150.2489	$150.25	$150.25	$150.20
Purchase #7	$20.81	9.354%	$22.7566	$22.76	$22.75	$22.80
7 purchase totals =	$469.00		$498.8994	$498.91	$498.90	$498.80