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	$145.70	10.790%	$161.421	$161.42	$161.40	$161.40
Purchase #2	$132.94	8.239%	$143.8929	$143.89	$143.90	$143.90
Purchase #3	$85.78	10.646%	$94.9121	$94.91	$94.90	$94.90
Purchase #4	$244.76	7.556%	$263.2541	$263.25	$263.25	$263.30
Purchase #5	$184.54	8.825%	$200.8257	$200.83	$200.85	$200.80
Purchase #6	$184.70	12.678%	$208.1163	$208.12	$208.10	$208.10
Purchase #7	$154.83	10.729%	$171.4417	$171.44	$171.45	$171.40
7 purchase totals =	$1,133.25		$1,243.8638	$1,243.86	$1,243.85	$1,243.80