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	$38.28	10.297%	$42.2217	$42.22	$42.20	$42.20
Purchase #2	$48.59	7.753%	$52.3572	$52.36	$52.35	$52.40
Purchase #3	$148.35	10.779%	$164.3406	$164.34	$164.35	$164.30
Purchase #4	$19.88	7.335%	$21.3382	$21.34	$21.35	$21.30
Purchase #5	$106.28	3.187%	$109.6671	$109.67	$109.65	$109.70
Purchase #6	$130.85	5.405%	$137.9224	$137.92	$137.90	$137.90
Purchase #7	$215.93	7.670%	$232.4918	$232.49	$232.50	$232.50
7 purchase totals =	$708.16		$760.3390	$760.34	$760.30	$760.30