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	$125.88	4.304%	$131.2979	$131.30	$131.30	$131.30
Purchase #2	$216.46	7.249%	$232.1512	$232.15	$232.15	$232.20
Purchase #3	$73.86	12.583%	$83.1538	$83.15	$83.15	$83.20
Purchase #4	$101.83	6.299%	$108.2443	$108.24	$108.25	$108.20
Purchase #5	$88.89	12.777%	$100.2475	$100.25	$100.25	$100.20
Purchase #6	$47.89	13.561%	$54.3844	$54.38	$54.40	$54.40
Purchase #7	$113.88	10.510%	$125.8488	$125.85	$125.85	$125.80
7 purchase totals =	$768.69		$835.3279	$835.32	$835.35	$835.30