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	$135.31	5.164%	$142.2974	$142.30	$142.30	$142.30
Purchase #2	$148.31	11.129%	$164.8154	$164.82	$164.80	$164.80
Purchase #3	$24.46	4.381%	$25.5316	$25.53	$25.55	$25.50
Purchase #4	$91.58	8.663%	$99.5136	$99.51	$99.50	$99.50
Purchase #5	$237.95	10.658%	$263.3107	$263.31	$263.30	$263.30
Purchase #6	$5.79	11.758%	$6.4708	$6.47	$6.45	$6.50
Purchase #7	$246.40	10.752%	$272.8929	$272.89	$272.90	$272.90
7 purchase totals =	$889.80		$974.8324	$974.83	$974.80	$974.80