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	$84.55	11.780%	$94.51	$94.51	$94.50	$94.50
Purchase #2	$156.90	4.254%	$163.5745	$163.57	$163.55	$163.60
Purchase #3	$180.28	5.129%	$189.5266	$189.53	$189.55	$189.50
Purchase #4	$100.30	9.393%	$109.7212	$109.72	$109.70	$109.70
Purchase #5	$165.79	4.302%	$172.9223	$172.92	$172.90	$172.90
Purchase #6	$93.63	10.741%	$103.6868	$103.69	$103.70	$103.70
Purchase #7	$28.94	13.436%	$32.8284	$32.83	$32.85	$32.80
7 purchase totals =	$810.39		$866.7698	$866.77	$866.75	$866.70