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	$18.25	3.550%	$18.8979	$18.90	$18.90	$18.90
Purchase #2	$78.82	9.333%	$86.1763	$86.18	$86.20	$86.20
Purchase #3	$67.60	12.546%	$76.0811	$76.08	$76.10	$76.10
Purchase #4	$168.49	12.806%	$190.0668	$190.07	$190.05	$190.10
Purchase #5	$141.33	10.742%	$156.5117	$156.51	$156.50	$156.50
Purchase #6	$205.58	10.591%	$227.353	$227.35	$227.35	$227.40
Purchase #7	$31.87	3.735%	$33.0603	$33.06	$33.05	$33.10
7 purchase totals =	$711.94		$788.1471	$788.15	$788.15	$788.30