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	$93.31	10.541%	$103.1458	$103.15	$103.15	$103.10
Purchase #2	$116.35	10.477%	$128.54	$128.54	$128.55	$128.50
Purchase #3	$163.89	13.801%	$186.5085	$186.51	$186.50	$186.50
Purchase #4	$242.28	7.320%	$260.0149	$260.01	$260.00	$260.00
Purchase #5	$110.41	9.506%	$120.9056	$120.91	$120.90	$120.90
Purchase #6	$92.61	5.675%	$97.8656	$97.87	$97.85	$97.90
Purchase #7	$127.93	7.846%	$137.9674	$137.97	$137.95	$138.00
7 purchase totals =	$946.78		$1,034.9478	$1,034.96	$1,034.90	$1,034.90