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	$125.46	4.808%	$131.4921	$131.49	$131.50	$131.50
Purchase #2	$65.30	11.503%	$72.8115	$72.81	$72.80	$72.80
Purchase #3	$64.31	9.281%	$70.2786	$70.28	$70.30	$70.30
Purchase #4	$81.83	10.558%	$90.4696	$90.47	$90.45	$90.50
Purchase #5	$219.58	8.353%	$237.9215	$237.92	$237.90	$237.90
Purchase #6	$92.53	12.873%	$104.4414	$104.44	$104.45	$104.40
Purchase #7	$124.27	3.120%	$128.1472	$128.15	$128.15	$128.10
7 purchase totals =	$773.28		$835.5619	$835.56	$835.55	$835.50