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	$244.54	10.588%	$270.4319	$270.43	$270.45	$270.40
Purchase #2	$109.86	10.236%	$121.1053	$121.11	$121.10	$121.10
Purchase #3	$191.53	4.664%	$200.463	$200.46	$200.45	$200.50
Purchase #4	$94.94	6.116%	$100.7465	$100.75	$100.75	$100.70
Purchase #5	$83.34	12.205%	$93.5116	$93.51	$93.50	$93.50
Purchase #6	$161.48	8.265%	$174.8263	$174.83	$174.85	$174.80
Purchase #7	$41.63	11.811%	$46.5469	$46.55	$46.55	$46.50
7 purchase totals =	$927.32		$1,007.6315	$1,007.64	$1,007.65	$1,007.50