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	$120.76	11.347%	$134.4626	$134.46	$134.45	$134.50
Purchase #2	$72.79	10.651%	$80.5429	$80.54	$80.55	$80.50
Purchase #3	$134.76	10.240%	$148.5594	$148.56	$148.55	$148.60
Purchase #4	$43.59	5.205%	$45.8589	$45.86	$45.85	$45.90
Purchase #5	$225.88	9.201%	$246.6632	$246.66	$246.65	$246.70
Purchase #6	$24.65	11.172%	$27.4039	$27.40	$27.40	$27.40
Purchase #7	$93.93	11.235%	$104.483	$104.48	$104.50	$104.50
7 purchase totals =	$716.36		$787.9739	$787.96	$787.95	$788.10