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	$87.85	3.459%	$90.8887	$90.89	$90.90	$90.90
Purchase #2	$38.96	5.131%	$40.959	$40.96	$40.95	$41.00
Purchase #3	$240.76	8.166%	$260.4205	$260.42	$260.40	$260.40
Purchase #4	$240.30	6.756%	$256.5347	$256.53	$256.55	$256.50
Purchase #5	$68.28	5.468%	$72.0136	$72.01	$72.00	$72.00
Purchase #6	$70.81	13.408%	$80.3042	$80.30	$80.30	$80.30
Purchase #7	$57.97	3.503%	$60.0007	$60.00	$60.00	$60.00
7 purchase totals =	$804.93		$861.1214	$861.11	$861.10	$861.10